I seem to recall reading something to that effect, but took it with a grain of salt. There were several patents, in Germany and elsewhere, for full auto Luger conversions, but none seem to have gone beyond the "one off" stage. I have no doubt that a "gangster gunsmith" could make such a conversion, and there were some M1911s so converted in the gangster era, but a full auto pistol, even with a shoulder stock, is not very practical.
The FBI collection has a couple of M1911 pistols converted to full auto, apparently more for psychological effect than any practical use, but I don't recall any Lugers. Full auto pistols are uncontrollable, even with a shoulder stock. I have fired Mausers, Spanish Astras, and several miscellaneous conversions, including two M1911 conversions (all legally owned, BTW). None would hit anything beyond the first or second round.