Staying cool in a wetsuit

Since I'm fairly new to kayak fishing and am still trying to figure things out, how do you wetsuit wearers prevent overheating? I went out at the end of December at pillar point and nearly passed out from heat exhaustion, the wetsuit combined with a well fitted pfd had me dying in the sun. I can only imagine how a nice summers day would make me feel.
Since I already own a bunch of wetsuits I don't want to throw down a bunch of cash for a drysuit?
Any ideas guys?

3 Mil Farmer Johns should work. 

Put a measuring cup on a string and pour water on yourself as you get heated, works fine for summers up here in a surfing 3/4 mil with pfd on. Now we don’t hit the 100* mark but you’d likely be colder then me down here as we’re ised to different temps.

I splash water on myself and put my legs in the water when I get hot. That keeps me cool in my 5 mil farmer john.

I'm going to guess you were in a full wetsuit if you were that hot??  Farmer johns should help a bit with that. 

 I wear a five mil wetsuit pants and 1.5 mil top and carry a 3 mil wetsuit jacket for when it gets colder. I also wear thin neoprene socks under my wet boots

Pee in it

Gross

In addition to pouring water on myself when it gets too hot, I wear a lightweight and light-colored nylon fishing shirt and nylon fishing pants - the really thin and lightweight sun-blocking stuff folks use in the tropics - over the wetsuit.  They help keep the direct sun off the wetsuit and help a lot with keeping me feeling cool.

Mine are made by Columbia but there are both less expensive and more expensive brands.

Pee in it

You gotta pee in it to stay warm.  Maybe he needs to stop peeing in it so he doesn’t overheat.   

I avoid overheating by living on the Mendocino coast. It's a rare day when temps get over 70 on the water up here.

I had no problem peeing in my wetsuit when I surf, at least it gets constantly rinsed but in a kayak hell no! maybe I'll cut off the sleeves on my older least used wetsuit.
Thanks for the suggestions.

When I started kayak fishing, I wore an old surfing 3/4, but the action at the shoulders was too tight compared to surfing without water under the rubber, so I cut the arms off and it was pretty good, even if it looked rough. I even sewed in a velcro relief slit. 
   When it nearly fell apart, I got an NRS farmer john, but was almost always cold and had cold feet with surfing booties.
Now I've got it dialed, at least for me (I get cold easily when sitting still and don't have much blubber.) and at least in SC/ Mntry:  two sets of polypro long johns, and one fleece rash guard (Mysterioso) under farmer john. Pull the John over the long johns after tucking johns into thin liner socks, then neoprene socks, then diving booties (Camaro).  If it's cold, I'll pull a NRS thin neoprene/spandex top (maybe equivalent to 1 mm) over the top of the farmer john, and if it's really cold (rarely), a thin fleece pullover under that.  Then goretex splash pants and top - these keep the water evaporation down on the wetsuit, and the hooks don't snag it as much as the wet suit.  Yes, I've tested self-rescue with all that stuff on.  But it is a booger cleaning/drying it - I just throw it all in the washing machine on gentle cycle and hang it to dry - if wet outside, just drip dry on hangers then into my water heater closet. 

When I started out I was wearing a full 3/2 full wetsuit and quickly found that was way too hot for above the water activities. I switched to a 3mm farmer john and at the time wore a rash guard made for under the wetsuit. I improved on that and still wear a farmer john, but now wear a loose-fitting spf rated sun shirt over the wetsuit on most days-I just find for me it's more comfortable and less restrictive than having it inside. I usually have a backup splash jacket to pull on if it ends up getting sporty out there. I have a one piece Kokatat paddle suit with a light wicking base layer underneath for the snotty days but have also found on the warmer days that I heat up pretty quickly in that too-like wearing a hefty bag in the sun. I have worn waders too which is the most comfortable, but also the riskiest and not recommended in case you go over. You should always dress for the occasion. It sounds like you have some time in the water if you own multiple suits, but if you're new to the sport and fishing in the waters off central-northern California and don't want to throw down for the paddle suit, then you should probably go with the farmer john. Maybe consider modifying one of your suits by cutting off the arms, or just throw down on a 3mm farmer john from Stolquist or NRS or one of the many others. The same thing goes for the feet, a pair of 3mm neoprene booties should be fine. You might consider how tight you have your pfd, it a personal choice as to how tight you cinch that up. Have someone pull up on the shoulders of your pfd from behind, you don't want it riding up over your head, and you do want it snug, but you also need to be able to breathe during activity. Other things to think about- Hat, sunblock, water, handheld marine vhf radio(know common frequencies), water, compass, fishfinder w/gps or handheld gps, knife, pliers, gaff, game clip, small first aid kit, check the forecast, swell, swell direction, tides.....fish with a buddy or file a float plan with someone you know or a harbor master.
PS- I would never pee inside my wetsuit unless I was surfing or in the water, which is also why I buy my farmer johns with a two-way zip or have a horizontal zipper installed in anything that doesn't...Cheers and good luck!

FWIW - I made a set of high waist pants out of an old 4/3 surfing wetsuit that I pair with a front zip wetsuit jacket from O'neil's. As others have said - splashing water is a quick way to cool down. Dangling feet in the water will also pull a lot of heat out of you quickly. I can also vent my top half a little with the jacket zipper. The two piece setup also makes it easy to take a piss on the water. 

Cheers,
Brad