Good question. The LEM was developed after HK's disastrous first attempt at jumping on the "DAO" bandwagon to sell hardware to the multitude of clueless US police administrators. Known as the V7, it was/is, without doubt, the most egregious trigger _I_ have ever tried on a handgun (if you have a LEM, pull the trigger on an empty chamber, and then pull it again without cycling the slide. Imagine doubling THAT, if you can, and you have HK's original V7). Needless to say, they didn't sell many of them. I have seen exactly two in my travels, etc.
Thing is, I'm not sure exactly when the LEM appeared. I want to say post-2000, but I just don't know for certain.
But, in any event, you'd be flirting with the spirit of the game. While the USP "officially" was launched in 1993 or so, they really didn't get out there in any numbers until quite a while after that. IIRC, it was 1995 before I even was able to put my hands on one.
For me, I'd have the same problem I had with the P226; small hands. If Sig hadn't come up with the short trigger when they did, I would have had to settle for a 5906. On the one hand, that boat anchor would have served me adequately. On the other hand… well, I'd rather not think about the other hand…