I have a butane torch. I was surprised how quickly it softened. I played with closing the ends as you say by twirling and letting gravity shape it. Made some kind of neat shapes but the heat of the softened glass was too much for the Silver NR wire to withstandI tried to find one of Dan's posts where he mentioned some kind of sealant goo (silicone or epoxy?) that was safe and heat resistant. I may also look for some Nickel NR wire (melting point 1453°C) that would work great with closing the glass.
High Temperature Adhesives and Epoxies, Ceramics, Insulation, Epoxies and Epoxy
not sure how thick these are but could probably use one of these in a similar fashion as the enamel idea too. Note that one of these is conductive.