Sugar water?! Wow, back in the day we used to use SALT (ALOT of it too). I dont know how old the vending machines you guys are working with are, but around here they are getting more high tech and no water tricks work.
However, if you guys still are working with the older machines I have a few master keys which let you OPEN the machines up for your gratification which I might sell. Though they are only for the Pepsi machines... meaning it opens up: Aquafina, Tropicana, Lipton Iced Tea, Mountain Dew... and whatever else Pepsi owns. Wont work for Coke branded stuff