If you have ever tried to glue something to glass, you know that it doesn't take much to pull the glue off (the set up type of adhesive or hot melt glue). The glass is slick and non-porous. Use a small amount of alcohol to clean the glass surface, let it dry completely then peel off a piece of satin finish "Scotch" tape, the type you use on Christmas packages and apply it to the clean spot on the glass where you want to glue. Now, put your glue on the tape and it will stick to the tape where it wouldn't on the glass otherwise. When you want to remove the glue, just peel the tape off. This is handy for many applications.