Well, the rules already cover how much a "drink" is...I believe (and im not looking at the book right now) that it is defined as "however much you can drink with one move-equivalent action." So really, you shouldn't be able to concentrate the alcohol in order to get the benefit of multiple drinks with one swig. However, when I had a drunken master a while back, the DM and I agreed on a few alterations that we thought fit the flavor and yet did not make the character appreciably more powerful. First, we allowed an item similar to the jug with the infinite water in it (brain fart, can't remember it's name), only with wine, so I could use it to drink in combat. Also, we agreed that during a full attack action I could use one of my attacks to take a drink rather than making an attack. With monk's getting multiple attacks rather quickly, and with their last couple attacks not having an incredible chance of hitting, this is a pretty good solution for both the monk and the DM, I think, and though using the last attack to make a drink each round is a little cheesy (I agreed with my DM that I would not make a practice out of doing this), as you say the character is a little less powerful so it's probably okay if you let him do that.