Thursthouse
Tight Loins
If only some genius would invent a fishing diaper. Oh wait, you did.
Seriously that's the answer. Taking all that gear off to piss sucks. Leaving the river sucks. Pissing on your waders sucks. Literally everything about pissing while fishing sucks. The diaper would take care of all of it at once.
In the meantime, the specific problem you're having is really about the last few drips, which never seem to clear the rolled down front of waders, even if you have an enormous thermometer dick like WDLuver.
The trick is to jump backwards with both feet right as you finish. With practice it can be done.
Precisely why I bought an Amadeu patch