"Semi-rigid" is tough. That's my big complaint with conforming clothing; it is sort of an all-or-nothing issue. Either an item stretches like rubber, or it doesn't. That said, I've been toying with something called "conformal" clothing; using ERC, morphs, body handles, phantom parts, in an effort to have clothing that moves partially or stiffly. You can of course do a lot with joint parameters, particularly fall-off zones. That and careful grouping, of course. For instance, for a holster I'd suggest making the belt part an ordinary conforming clothing, but the holster itself an additional body part with "Bending" switched off.