Was trying to do that yesterday but the computer I was at has a broken key and I use my paste function to type 'm'. Makes it difficult to copy/paste. Plus, it appears that the store has different variations on the paintball regulator or adapter which I didn't know till just now.
http://www.homebrewing.org/search.asp?keyword=paintball
If you're looking at the bulk fill adapter, that's made to fit onto a paintball tank. Not a 5 gallon tank. What you would wind up having to do is cut the air line on the bulk fill adapter, and attach it to your larger regulator (meaning you would lose the connection to your ball/pin lock).
It appears that the valve that allows incremental releases of co2 to fire rounds is built into the airsoft/paintball gun/marker, not a function of the cartridge. Once you pierce the cartridge all the co2 is released (which is what happens in a seltzer bottle, or when launching a co2 model car)
Without going through full prices, you would wind up needing: paintball tank (20-30 bucks), paintball tank regulator (90 bucks), or normal regulator and adapter to fit a paintball tank, and a bulk fill adapter. (how much was that one? 50?). Unless there was a reason to use a seltzer bottle a whole heck of a lot, I think I'll stick with cartridges. Now if I were a resturant that served via seltzer bottles in order to be fancy, I'd reconsider. This would be the sort of place where $50 per plate is the norm anyways and you're expecting some sort of perrier style water.
Also... it appears that there's another problem...
The Drozd uses a standard 12gram charger, which seems to be a general standard for airsoft guns and paintball markers. A selzter bottle generally takes a 8 gram charger. So you'll have to also figure a way around that size difference, unless you have one that takes a 12 gram.
I actually have 2-3 (I swear I had a 3rd somewhere around here) carbonation caps, so I have at least 2 bottles of carbonated water ready and several closed cold bottles. I'd drag those instead. If I were having a cocktail party where carbonated water is used in the drinks and we were using expensive alcohol, I'd probably use the seltzer bottle to be fancy with chargers. If we're already spending money on alcohols, the minor dollar per small water is nothing and it'd barely be used except for something like an old-fashioned. If we're doing a every day/weekend drinking party, I just charge the bottles, recap, and drag the bottles in (in case they get tossed.)