I use metal water bottles as well, both Kleen Kanteens and Guyot Designs bottles. Most of the time I don't really see a need for dedicated bail. My multi-tool or gloved hands work just fine for placing and removing the bottle from a heat source.

With that said, there are bail designs out there and even a few that are being sold:

http://jerkingthetrigger.com/blog/2010/10/09/review-marion-outdoors-flexible-bail-for-guyot-bottles/