Well, there are two major problems I have here. First, Boston doesn't need a backup PG. They have one of hte best in the league in Jason Terry.
But if you argument is that Jason Terry isn't really a PG...well, fine, then Jimmer Fredette isn't one either.
I am more open than most to trading Bradley, because I think he might be closer to his ceiling than others, and that his value will drop as other GMs realize this. But not for a guy like Fredette who is really a questionable NBA player at this point.