We modders tried various ways to make holsters; a generic apparel item sized to fit most handguns, clever usage of armor addons, etc.
But (unless I'm late to the party :unsure: ) the answer may have been right under our noses the whole time: Backpack nodes.
Upon dissecting the Katana mesh in GRA, I discovered how they got the scabbard to work within an individual nif, without need for armor addons or any of that stuff. Lo and behold, a Backpack node, and all the various setup parts.
Inspired, I decided to try it myself. I unburied my http://www.fallout3nexus.com/downloads/file.php?id=8751 mesh from FO3 and went to work.
On a technical level, it was a success: the mesh properly appeared and moved in sync with the pelvis bone as was intended.
However... my alignment of the mesh was considerably off. I thought it'd be as simple as just positioning the holster mesh in nifskope opposite the katana scabbard mesh used as a reference.
Instead... http://img195.imageshack.us/img195/5599/magnumholsterpocoops.jpg. :facepalm: :lmao:
I'll get to figuring out how to align it tomorrow. For now... sleep.