Hi Patrice,
Brent showed us a trick while he was in town last weekend. He just decorated a large paddle on the end of the rod, heated and stretched, and formed it over the barrel of the torch. It was closer to a bracelet size, but I would think the same technique would work on your ring mandrel. NO RELEASE. Yippee!
Maybe you could punty up to the back (or front) of the ring and weld the bottom together. I'm sure someone with more experience with boro can jump in and give you better instructions.
Some of the students came out with some cool boro rings, though!!!
If you ever have the chance, take a class with him. I think I'm hooked on boro now, too!!