Nope, the slide cut where the cartridge fits under the extractor is too narrow. You can convert the .40 to 9mm because the smaller 9mm cartridge will fit -- its a little sloppy which leads to erratic ejection and the occasional stovepipe, but its a viable alternative for shooting cheaper practice ammo.
I've got a 9mm barrel (from S&W via Midway) for my M&P 40C and a threaded 9mm Storm Lake 9mm conversion for my M&P 40. Both work well with the above caveats.