According to BATF: no.

The Bushmaster/Rock River design isn't just a standard collapsable stock that's been pinned open; it has a full-length receiver extension that doesn't collapse.  In addition, the stock has been blind-pinned in place by 5 pins.

Now, some people HAVE uses the multiple-blind-pin method, usually along with JB Weld or some similar "glue", to fix in place a collapsable stock.  All I can tell you is that BATF has rejected every one of these that had been submitted, though theoretically, they'll review your design.  Of course, getting busted for such a stock would be pretty rare in today's environment, but with Project Exile rolling out nationwide, who knows about tomorrow?

-Troy