Traveling to Washington a few weeks ago with 2 ladies I came up with a solution to making pit stops every 25 minutes.
Men urinate by use of muscular contractions. Therefor we can piss a good 50 or 60 feet, write or names in snow, go against the wind and other party tricks.
Women urinate by gravity and have to hold it in with muscle similar to a pinched off hose.
So a theory we came up with to stop the constant pit stops. Simply ask your female passenger to put her head on the floor and knees on the seat. This is like turning the bottle up instead of down.
I haven't tried it yet but it is a theory and I think it will work. Maybe some have tried.
"Women cannot urinate when turned up side down."