to the OP.
The idea of meeting him out of state is a good one. VT has been mentioned. Just be aware that RI and NH are also legal.
Also, if he was on his way to NH or VT and you happened to meet him along his route while he was in MA and took possession of the guns then, he'd be fine. He can possess the guns in MA legally, as long as his destination is not in MA.
Simple huh?
that's walking the fine line. The cop could claim it was pre-arranged and the actual destination was MA. It would be significantly more legal to do the hand off out of state.