If the missing pad is on pins 3 or 5, don't worry; those pins are not used. If it is pin 2, be careful inserting the socket so that the solder-side pad is not damaged, and solder it on the bottom. If the bottom side trace on pin 2 is damaged, solder a jumper wire between pin 2 and the green LED next to the opto, replacing the trace.
If the damage is to pads 1, 4, or 6 on the top, the easiest way to deal with that is to carefully scrape off the solder mask on the trace where it connected to the pad, bend the socket's pin so it sticks straight out the side of the socket, and solder it to the scraped-off section of trace.
/mike