Can't answer your exact question, but here is a configuration I learned of while talking to Rick @ Gray Guns about getting a LEM trigger in the P30 I am going to purchase (eventually).
Rick said it's possible to install the LEM trigger kit on a P30 V3, and retain the de-cocking lever. That way you can have it either way. You can choose to run the pistol LEM fashion only, or use the de-cocking lever to de-cock it whenever you want, which would bring it back to DA for next shot then LEM afterwards. He also said it is possible to either remove or retain the safety lever.
He said the kit comes with a plug for the safety lever hole if you remove it, but if you remove the de-cockng lever, there will be a space left where it resided.
I may be wrong, but am assuming this could also be done on your USP