Ok it looks ok, don't take this in offense but i think it's a bit strange..
Anyway, here is what I would do.
Dis assemble your PSP (take the faceplate off)
take the butons. pull or cut them off the rubber. <<< no sure if that pert is necessary try it for yourself. Then get a hot glue gun, heat it up, while it's heating cut your Xbox button(s) up to about here:
, then measure the right size drill bit, drill hole in the faceplate from the bottom out the size of the xbox buttons, now that the hot glue gun is hot and your faceplate and buttons are done, now you have to do this quick, (not sure but the buttons look hollow at least a little) ok, add some glue to the bottom of all the buttons then before the glue dries stick them on the rubber then when it dries hit the base of all the buttons with a bead of glue all the way around. Once done, put the buttons back on and faceplate. Enjoy!