Even if it were okay to do this (which it isn't), I guess the resulting "pistol" would be horribly imbalanced, both from a weight distribution point of view and aesthetically. Thankfully the 2240 pistol can still be had cheaply new, so better to go that route.
I've gone the other way with one of my 2240s......shoulder stock, steel breech and red dot sight, but kept it at legal pistol power. Still makes for a fun "mini-carbine" for short range fun.