Not sure...do the electrical approaches to this problem still work if the battery is totally disconnected? Ie, there's no longer any complete circuit? Maybe, I don't know..
In any case, if you need to do the mechanical approach, this will give some guidance..
http://986forum.com/forums/boxster-general-discussions/63915-help-disconnected-battery-closed-hood-jumper-method-doesnt-work.html