There are velcro straps sold in home improvement stores. One side is hook, the other is fuzzy. They look sort of like wristwatch bands. They're excellent for strapping in LiPos. I'll see if I can find a picture online.

.... oh yeah, you attach them to the model "permanently" and they make it quite easy to position the battery without having to deal with positioning them. Also, you can use a very small patch of velcro on the batteries to mate with the band when it's strapped closed and the battery is held very securely.