As far as I am aware you cannot. As in the service menu it says not allowed you cannot even if you are sim unlocked. It is a hardware limitation. Sorry :smileysad:.
Unlocking the bootloader is risky anyway, my Xperia L reports that I am allowed but I do not plan to do so until Sony 'ditch' the Xperia L, sometime in the near future I guess :smileyshocked:.
