Learned lots today; HDR and fabric doesn't get along very well. Natural fibers are the worst - the weave becomes emphasized to a huge degree, and really wrecks the illusion of scale. My initial idea was kind of a greasy leather thing - that's out. Leather doesn't make sharp enough folds, and it's obvious it's leather. Which wrecks the illusion.
Suprisingly, it's synthetic fibers which work best. Fibers with an extremely tiny weave, but not shiny.
I'm off to the fabric store tommorrow morning, armed with dozens of HDR fabric test shots.