I have a Safariland 6004 for my USP Tactical, and I got my HK45 in tonight.
I figured I'd go ahead and throw it in there, and low and behold, its a pretty damn good fit.
The holster I have is a 6004-92-121 (right hand for USP 9/40/45)
Note this is for COCKED AND LOCKED carry. I have no idea if a regular USP holster will work, but if you are looking to carry your HK45 in a SLS type holster with no light, and condition one, this will work for you.
The top screw (the one by the trigger guard) needs to be loosened pretty good for it to slide in and out with relative ease, but once its where it needs to be its pretty smooth, and still gives a good amount of side to side tension to keep it in place.
The SLS hood is tight, but it will lock into place. It wouldn't hurt to remove 1/16th of an inch of material near where the hammer and SLS touch to ensure a reliable lock of the SLS.
I figured it would be close, but I didnt think it would be THIS close. Its almost a perfect fit.
For those of you that need a quick fix, this should work nicely for ya.