One idea I had was to mount them on shrink film. The speaker's panel could be made out of a 1x2 frame, simialr to a knitting frame, with the film mounted in the frame sandwich. The film could then be shrunk with a hot air dryer or larger air heater, for more uniform shrinkage.

I've worked with this type of film in the past when I was in the packaging industry, and there are all kids of chemistries used. Also, you can get uni- or biaxially shrink characteristics. The film comes in rolls of 36" wide and miles long. You might do a google search to see if a film supplier can give you free samples. Look for films such as PVC, PVDC, PET, OPS or PE. A quick test might be to pick up a window winterizing kit from a local home store. This is PE (polyethylene) and has marginal dimensional shrink, but as long as you can get it tight it would be a fun experiment. Other films have up to 80% shrink.....Colin