The ZRL protocol of having you video yourself weighing yourself, then weighing some object (a weight, a gallon of water), then weighing yourself with the weight, then measuring your height all in one continuous video within 12 hours before or after your race is better than nothing, but I did a light 40 minute ride before bed last night and didn't drink as much as usual during the ride (didn't feel like I was working much) and my scales said I weighed ~1.5 lbs less this morning when I weighed myself than I did yesterday morning (drank a typical amount during the 3 laps of Whole Lotta Lava the night before), so, as you say, there is lots of room for gamesmanship. Of course, I'm a fatty, so there's a lot more room for play in my numbers (and small changes have less of an effect) than you folks with typical cyclists' bodies.