My understanding is like MMs, that men just lift the inside leg of their short legs up and "manouvre" themselves down and out the edge - whether on the bike or off - bib shorts are irrelevant.
Bike protocol says you should go to the back if you're not getting off.

And I have heard that on a race like the current Tour, if you need to do "#2s" and you can't stop and go behind a tree, then the team car hands you a baseball cap, which you skoot down the back of your pants, and when you are done you hand them back the now somewhat heavier and smellier cap.
Just what I have heard, I stand to be corrected.

I guess women who have a wee on the bike are set up differently to me because I honestly don't think my muscles would let me - and yeah, if I could, I'd prolly only do it in the rain... men might be able to pee down their legs, but we'd have to pee through the chamois...