I think we may have something to learn from hookah-smoking adepts. I'm a huge fan of the hookah and upon doing research and talking to avid hookah smokers (and I'm talking the real shit, not some all-glass-rubber-hose garbage or shitass Hookah Brothers hookahs), I learned that they use several different recipies for the hookah water. Often they use spices, lemon water, things of that nature. What I love, when smoking hookah, is using a milk & icewater mix (you need to heavily dilute milk or it bubbles up). This might work well as bongwater - it really smoothes out the hookah smoke.
I think people exaggerate the solubility of THC in fats and alcohol - "highly soluble" doesn't necessarily mean "quickly soluble." I was worried that a shisha (molasses tobacco) & pot mix wouldn't get me as high because of the fat in milk absorbing THC, but it worked fine. I'd be interested to see how this combo works in a regular waterbong. For hookah I use maybe 1 part milk to 10 parts icewater, and this still bubbles up a bit, so experiment with ratios.