>I think you could get almost the same effect by just using an external reservoir of fake pee (or real pee) with a pipe running into your pants.
Now this is an idea. If you wanted the constant dribbling experience, you would need to find a way to have it empty very slowly, but I dont think that would be too hard. Just having it randomly empty would be easier probably, just have a little micro-controller and a valve like was mentioned before. I think getting the temperature right would be important to the experience too, especially if you wanted to simulate unexpectedly losing control all at once instead of slow dribbling. Either having it go off fairly close to when you fill it up, or having a little thermostat and heater of some sort would solve that though. The only other thing to deal with is how to mount it in a way that doesnt feel disruptive, but I dont think that would be too hard with a little creativity.
Instead of purposely drinking more, you might want to deliberately drink less so you wont have to go much at all, as that might sort of break the illusion.
Also, if diapers were involved, water would let you "use" the diapers more than pee normally would, as it has less salt and all that in it.