When I installed windows 7 I opted to do a fresh clean install, but the key I purchased was an upgrade key and required that I performed an upgrade. The disk itself was bootable so I performed a clean install and modified some registry keys and ran a vb script in the system32 folder and this enabled me to enter my upgrade key to activate window even though the system knew I performed a clean install.
This isn't illegal, Its just a workaround. Since I had a legal copy of windows to upgrade from, I didn't break the EULA. I decided to automate this by writing a little application that applies the patch automatically. I am 90% sure it works, but I can't test it. So if anyone out there is about to install windows 7 with a clean install from an upgrade key. Please try out my patch and tell me if it works!