My sorority has almost always had some sort of glass as favors at formals. The general rule has been, don't drink alcohol out of them publicly. Typically we would have a "champagne" toast at formals, with non-alcoholic cider, in our engraved "champagne" flutes, then take them home. We never had alcohol at any of our events anyway - per national policy.
You can't stop people from using the glasses for alcohol in private. For a while, the only champagne flutes my husband and I had were the two we got at my AEPhi senior formal. But it was just the two of us, so who cared?
This won't solve your chapter's immediate problem - but in future you may wish to get glasses that don't have an immediate "alcohol" connotation. No shot glasses, martini glasses, etc. Instead, get pint glasses or highball glasses (they can be used for water or soda) or coffee mugs. You could even contend that the beer steins can be used as coffee mugs... my husband has a "beer" stein from his professional fraternity, that he uses for coffee.
JMO.
