Go to MSDN, look up the SHA-1 hash value of an ISO with Update 1 (you don't need a subscription to look at that information). Google that hash value, find a download for that ISO, download it, verify hash (using something like HashCheck), and you're done--no fiddling with that stupid setup downloader.
I really don't get the point of Microsoft making these ISO downloads hard to get. All that it's doing is making it harder for legitimate users to reinstall. You'll still need a valid key, and you'll still have to go through product activation, so there are still robust piracy safeguards in place. So I say "screw it"; you apparently already have a legitimate license, so you have the right to to acquire a copy of the ISO.