I was going to suggest the same thing - look at the glider fraternity.
The glider fraternity have an additional problem. Gliders need to have a very small cross-section to be aerodynamically efficient. This results in a near-flat pilot position, with the pilots knees typically well above his/her butt. In fact, your butt will rest into a - for lack of a better word - butt-well. This means that any open system, that relies on gravity (like peeing in a bottle) will not work. Because there's simply no space below your butt to put the bottle.
Various solutions have been tried with more or less success, and sometimes hilarious results (but you'd have to go to a gliding bar to hear those stories). By far the easiest, cheapest and least risky solution seems to be adult diapers. Available from your local pharmacy under the "incontinence" section.