reset ios6 user data without doing a factory reset

[Golf1.6]

I intend to sell my iphone 3gs with ios6 as a jailbroken device. I dopn't think the most recent iOS is jailbreakable so it needs to stay on ios6.

Trouble is the one way I can think of resetting the handset is to to do a full uprade of files and choose not to restore immediately.

Or is there another way>