I know some people who have had some luck getting 10-round .45 mags to work in .40s. Mec-Gar makes an 11-round .45 mag; I used to have one, and with a Pachmayr pad on it, it was 169mm long. I've seen some truly awful 11-round mags at gun shows, and hopefully they weren't Mec-Gar's current production. Maybe you could get 12 .40s in there?