.50AE from Alaska did it.
He did it on .40 USP. Reamed out the bbl, opened up the ejection port (elongated), and used Para (P16) mags. He also swapped the mag release for the one from .45 USP because of the metal mags. The slot for mag release needed to be cut in the middle of the Para mag bodies (take out the mag release, and use the grip as a template). He claimes that it works great. He quoted the maximum OAL cartridge length you could use, not sure how close it was to factory specs. I am betting at least 135 grainers would work without having to load your own. This guy was known on Shooters for liking to spice up the loads. So since he is still typing, I am guessing his USP is holding up well.
Of course you could do the same thing with 9X23 in 9mm gun.
I almost bought stainless USP .40 (no refinish needed after opening up the ejection port), just to try that. You can even use Olyarms bbl ($100) and ream it out, so that conversion is not permanent. Couldn't justify it, because you can do reverse with G-20/29 by just swapping for the .40 conversion bbl, no extra work/magazines involved.