The P30 LEM (and I would presume the P2000 LEM as well) cannot be converted to DA/SA since the factory LEM models lack the cutout in the rear of the frame for the decocker lever. The USPs had a truly universal frame and could thus be swapped to whichever variant you wanted.
That said, if you start with a V3 DA/SA P30, you can convert it to LEM and either just live with the gap in your frame or keep the decocker in there to create a "V0" LEM configuration.
edit: Dan beat me to it