We're talking about Vario-matic transmissions right? I saw them used on a build once on Scrapheap challenge (Junkyard wars to you guys):
http://en.wikipedia.org/wiki/Variomatic
The concept was very simple- the two opposing cones changed shape as the rpms increased, causing the drive ratio to alter as the belt shifted shape/posistion between the two cones which spin the belt. Seems the cones were made of a plastic that would deform naturally due to the centrigugal forces at higher rpms. I'd be lying if I said I hadn't though about this concpet for r/c use, just wouldn't really now how to make it a reality...