I would be surprised if any of these mass shooter types could. I don't think any of them can shoot so good either, but still very dangerous with a semi auto with a hi cap magazine.
I'd have to go look at the list...the ones that spring to mind probably couldn't...the crazies like Loughner and Lanza, no.
Cho, maybe. Joker, maybe.
It just depends on their level of determination and commitment.
It's not rocket science...I have no doubt I could do it with no special tools.
Cut the 10'ers apart and use the pieces to fabricate a longer magazine.
It might take some trial and error, adding and subtracting of spacing materials in the bottom, spring tension...but you've already got the mating for inside the receiver plus the follower...the hard part is done.