How to factory reset a locked Sony Xperia S

Bit of a dilemma, I have an old Sony Xperia S that I cannot get into as I can't remember the passcode to unlock it. I also cannot remember the gmail address that it was registered to so cannot reset the passcode that way. Anyone know of a way I can get into it? Or a method to factory reset without unlocking the phone? My iphone has failed on me, so currently phoneless!