Reminds me of when I was in the military and Marines gotta take a piss on a convoy or alternatively a lazy Marine in the field that doesn't want to get dressed to make their way to the piss tube (Especially when it is cold as balls in the Sahl Sinjar desert).
I guess what I'm saying is there is no shame in pissing in a bottle. Just make sure you get rid of it properly especially before your car gets hot. Last thing you need on your hands is a pressurized piss bottle.