Yes, a phat pandoras CAN be used on a slim. Mind you the other way around will cause a brick. Now what you need to do is use the JigKick (pandoras) batter and the MMS to run Despertar del Cementario. That should do the trick.

OR There is a different easier way. I can go into that if you want?

Oh and before you try this tell me what PSP he has. Such as a vader, god of war, is it old is it new. That stuff. I need to tell you if you have the incompatable motherboard before you waste your time and get bricked.