This one is as neat as teats on a mother cat :
http://v3.espacenet.com/pdfdoc?DB=EPODOC&IDX=US1367996
It is a carbine-type stock that remote mountes the Luger trigger back to the stock area. This is way cool !!! But then you need to cut your trigger guard off the Luger...
Designed by Vvaldyslaw Sussman in New York in 1919/1921...