Most of the UK guys I know use Lastolite that is backlit. I've never tried backlit because I've never had the need. We've been very happy with a Denny's white vinyl. They run a 50% off sale on it every month or so. I've got lots of raw muslin and would have used it if I thought it would work better. However, it sounds like something you'll need to experiment with and let us know if it works great. Everyone here is always keen on new ways of doing things.
BTW, a white seamless is the cheapest and best way to shoot hikey - just need to wrestle with it a bit. We use our Denny's when doing preschools and the seamless could not take the wear & tear. We took over a thousand preschoolers sitting/standing on it (all lit with total of 2 umbrellas and 1 on camera flash set at 1/32 power) and it just wipes clean. Shadows were never a problem for us if placed correctly.
Our samples at
School & Grad - click on Premium Proof Gallery.
DougA