The OP seemed to be discussing writing up a conversion of Dragonstar to 4e by fans. I presumed he planned on putting this on a website as HTML or PDF rather then as a product (even a free one) in DriveThru or a hard copy.
The GSL wouldn't even apply unless he signs it, which as you pointed out he couldn't. But I don't think the OP was referring to a product as much as he was a fan project. If the fansite policy has similar clauses, then it would prevent it.
The issue of using FFG's IP would be between the OP and FFG; WotC, the GSL, and the fansite policy would not enter into that.