I love sharing things I've come up with and reading about your projects. Recently I had several lots of repair jewelry. I purchased some blank ring findings on eBay and glued on old buttons, single earrings, broken items. Voila! I have rings to go with every outfit. Make sure the surfaces you are joining are clean and grease free. The most important part is to choose your adhesives carefully. I don't think that hot glue is strong enough for this project. If I am using glass I would use E600 or silicone cement. Read the instructions on the adhesive carefully to make sure it is compatible with your material. You want the ring to be water resistant. Obviously it is better to use an object with a smooth back so there is no gap, but some adhesives will fill in gaps. Make sure they are as invisible as possible.
I had great fun doing this and hope you will, too! My favorite eBay seller for findings is A Button Lady.