Well after whitening my teeth, I reallized something. I think I can use the removable tip on the syringe from my tooth whitening kit.
I have one of those tooth whitening kits you get from your dentist. It's basically the one where your dentist takes a mold of your mouth and you get these plastic trays. You then use the gel and inject it onto the plastic mold. So anyway, it's the clear plastic ones. I think most of them are the same because my girlfriend has a kit as well and the brands are different, but the plastic syringe is the same. I'm not too sure though about off-the-shelf brands like Colgate and stuff.
All you have to do is take off the removable tip, chop off a 1/4 inch off the base so that it will fit over your duster nozzle and then chop off 1/2 inch off the tip. Make sure you have a really sharp knife or utility knife. Viola! Instant duster adapter. The nice thing is that it forms a tight seal around the gas nozzle on your GBB mags so there's no waste!
You can ask your friends or relatives that whiten their teeth for their syringes too. Although they may look at you funny :grin:
I guess the only drawback is if you smile during a game, you might be spotted
Sorry about the resolution, I just used my camera phone and it's not that great. But you get the point I guess.