Similarly, running in a sweat suit on a hot day should work well. However, it's important to refresh your natural salts, as sweat is not pure water. Get a posing suit long enough in advance so that you're comfortable in it, and not feeling embarassed when you get on stage. Get one custom made. Make sure the cut is exactly how you want it.
Physiques differ, and so do the appropriate styles of posing trunks.
Maybe get two pairs, just in case one gets dirty or covered with oils, etc. All this usually means that you'll also probably want to get rid of hair, unless you're lucky enough to be born without it. It took about 1.5 hrs for me, but I'm a lot more comfortable now in the posing suit. The next day you'll look like hell. Fortunately, these go away in about 2 days.