For Version 2, I deployed a piece of instant jewelry I’d brought on the trip. The two-finger ring became a perfect mount point for the battery pack, using some double-sided sticky tape. The tapes helped hold the ring on my hand, too.
It stuck on and didn’t short out in 95-degree weather at Maker Faire New York, and I consider that a success! The battery lasted for hours as we wandered the Faire and the city. I will definitely be using this again.
…In fact, I already have! Someone on reddit requested low-light pics/video, so I stuck it back on with double-sided tape. If your skin is especially sensitive, you might want to stick it to something else first, to weaken the tack. As-is, this worked great.