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I bet the good folks at Four Seasons in Wakefield could do it.
It's not going to be adjustable without modifying it drastically. Then depending on how its done it may or may not be legal. Those cripple stocks were not meant to be adjusted... ever.
You're better off just tossing the fake collapsible in the trash and putting something like a Sully or an ACE on the rifle that has varying size buttpads, etc, that can be screwed onto the back end.
-Mike
I am not quite sure of the best way to remove a roll pin...