I don't want to reduce the blockade issue to being one that only has one possible solution. I don't even want you to think that all you ideas so far have been useless- it is just that I see the Imperial players being able to see past it all (incidentally, looks like the Captainplayer will be doing the Squadron Leader's job, so you will be up against a player after all).
Let me put it this way- the chances of those freighters, slow and bulky as they are, flying past a pre-set Imperial blockade of three Star Destroyers and attendant fighters are about nil, whether you are with them or not. Chances are they'll just turn around and go home.
But concentrate on exactly what your objective is here. What are you, ultimately, trying to do, in reagrds to this specific blockade situation?