Brian used to own a Glock 29 (10mm Auto subcompact) and liked that he could conceal it easily but did not like the lower velocity, shorter sight radius or snappy recoil.
To fix the 29′s deficiencies he took a Glock 20 (full frame 10mm model) and use his stock reduction tool (hacksaw) to reduce the grip to the size of the 29′s grip. This allows it to use the 29′s 10 round magazine. In order to make it easier to hold, Brian ground up sandpaper and expoxyed it to the backstrap.
I think it is a very nifty DIY solution.
[ Many thanks to Brian for emailing me the photos. ]