I have a difficult time imagining any outsider who isn't familiar with our system stepping in at this point in time and being very effective. It's possible that my opinion is wrong, but that's how I personally see it, and also why we tend to go back to guys who are familiar with our system--veteran wise.
I think it's also why Belichick attempted to bring in Sanders with enough time to get the playbook down, go through all of the OTA's and the entire summer of TC. If a move like this were to be made, it'd have likely been made. Again, this is my opinion, but based off of what we've seen I tend to think it's more correct than not.
If we'd be bringing in an outsider now he'd probably just be for a depth signing, and possible even inactive some of the time or most of the time. Of course an argument could be made that he'd be able to slowly pick things up and make some plays down the stretch in the vein of a Jabar Gaffney postseason run 2006.