Until now - behold the Blackhawk Omnivore: HK USP + GGG Rail adapter + TLR1
Not the greatest design in the universe, but I really need a way to hold that gun in SHTF. Not worried about conceal. Just want it on me. Based on vids - looks like it really could hold nearly anything. Especially things with lights. The attach/lock point is actually the TLR1.

Dave - I have a Blackhawk Serpa in Carbon Fiber (with holster, paddle/belt attachments, and a mag-light holder as well) - let me know. Probably be great for your USP