Im in the same boat, however there looks like theres a workaround to it
run the setup so you have the extracted folder with the setup.exe file within it - this is actually a full installer disc.
the problem is building a bootable iso holding all these files. I couldnt get it work so instead I used my pendrive (4gb) and set my bios priority so that my USB is booted first.
the information to bootable USB is here: How to Install Windows 7 From USB Drive without Windows 7 ISO DVD
then just restart your pc and install custom!
ill report back when its fully installed and activated
I can confirm properly now that this method of install works and my machine is now activated!