I was going to suggest th wire frame with an open clasp in the back so you can fit it snuggly on your hips and take it off/pit it on most easily. However, you can also look into this thing called "fosshape" http://www.dazian.com/html/fosshape.html
Then you just make a base for it and it has a LITTLE flexibility. If you use the Fosshape, the you should do one of two things: Make it in two peices (front/back) and fasten them to eachother with clasps hidden around the hips, or build the front on a regular belt that you can wear backwards so the clasp is on the back. The main thing you have to think about is taking it off and putting it on. It doesn't matter how good it looks if you cant get it on.
I'm using the first option with Fosshape to make a belt for Sylvanas which is a belt with a similar principal so I thought I would shoot my findings your way~