I usually do this with a new install, so I drill the stock and the pad for two small dowels then grind the pad to match the stock then glue.
I suppose you would have to use a couple of 1/16 or 3/32 drill bits, drill through the pad into the stock, leave them sticking out of the pad enough to line the pad up with the holes in the stock, glue, let set set for a few minutes then remove the drill bits.
Will leave two small marks in the pad though.
The only other way that comes to mind would be to wrap a piece of card board (like a legal tablet back), or thin plastic, tightly around the stock and protruding beyond the end of the stock a 1/4" or so to align the pad. Clamp the card board in place and glue.