Im a little surprised that you have gotten more than a couple inquirys.
In my recollection, the only people that really seemed to care about who was or wasn't drinking were alcoholics.
I have a friend who is Mormon, and he doesn't drink, never has. He does a lot of high level corporate events and everyone else drinks.
There really is something about a couple guys sharing a beer as a bonding thing. I hate it, but its true.
I kind of felt that was less prevalent with women, but perhaps Im wrong.
Simply saying, I just don't care for it should suffice 99.9% of the time.
If it is someone that you used to drink with, perhaps you could say, doctors orders? Or just say you cant? Again, in a business setting, I would have a hard time imagining anyone pressing too hard.