OK here you go. I've done it a couple of times now using
WP7 Registry tweak
(
http://xdaforums.com/showthread.php?t=907971)
To activate MS Activation Code so you don't have add it manually each time use the following (obviously you need to have an Activation Code first)
Code:
REGEDIT4
[HKEY_LOCAL_MACHINE\Software\Microsoft\GwpCPC]
"ActivationCode"="*****-*****-*****-*****-*****"
But take care with the code ActivationCode"="*****-*****-*****-*****-*****"
The "-" are not underscore "_", though they look like it, but dashes "-" (hyphens) - I got caught with this.
Run MS Activation Code before logging into to Live/Marketplace. Works a treat and skips the Live Code step. Obviously need the code first.
You can then use it more than once, each time your hard reset for example.