I have heard from my partner that some of the men in one of his training packs can do it on their bikes as they ride...

Personally this has never appealed to me.

I have been fortunate enough not to HAVE to go durng an endurance ride, but I guess I will need to one day... and then I think I will choose to squat and pee... don't think I could bring myself to pee as I ride, or leaning against a tree...