I sweat more than a two dollar (fill in the blank) on nickle night

That's funny.

According to your logs you're well seasoned.  A camel pack may be good for you.  With your condition all I can say is hydrate well.  Experiment with quantities.  You may be able to absorb more than a liter/hour.  Drink as much as you can and still stay below the nausea line. You probably won't be able to reach equilibrium of drinking/fluid loss but you can catch up in your off time.  Urine color is a pretty good guide to hydration = it should be clear enough that you could read a newspaper through it if you peed in a glass = just light yellow.  Sorry I got no silver bullet for ya.

I'm in your boat, and hope you find a better solution than I did - when I did a 70.3 last year in the summer heat, I drank 8L (4gal) over the 5 hours, but still ended up weighing in post-race 5-6lbs less than I did that morning.  Didn't pee once, and that post-race weigh-in included post-race food.  Also, I blew up on the run, but there's a possibility it was pacing-related.

I carried 2 frame bottles on my bike, 1 aero bottle (total: 2L), and refilled with about 1.5L on the course.  On the run, I partook in 1 water and 1 gatorade (assumed to be about 250-350mL total) at each of the 11 aid stations.  I also had a full bottle of gatorade during T1 and T2.  Post-race, I was pretty lightheaded and getting headrushes, which I fixed with more hydration.  It is possible I wasn't getting enough salt, but I wasn't getting cramps, I was just dead and hot.

During training, I've measured my loss rate at 2.0-2.5L/hr (1.3lbs/15 minutes) in summer temperatures, and my race was probably one of the hottest days all last summer.

Solution: I'm just sticking to short races from now on.