Poking around for battery extender solutions, I came across these, which both purport to offer a bit of cushioning as well.
http://www.amazon.com/FASTMAC-CiV-0100-Battery-Charger-iPhone/dp/B001N5RDRY
https://www.amazon.com/dp/B001E42QBW

I think I'm going to get the first, which while having less of a cushion function, appears from customer reviews to be a more robust battery solution. More news when I have it...