How to solder this pin
It all depends how important this customer is to you. This is a fix that can only be done in a very messy way, as in it won't look very professional. Find out how important it is to have this fixed, tell the customer that if it was fixed, the damage is great enough that reliability will suffer because of it, and your company cannot offer a guarantee etc so you cover your own backs. If they insist they want it fixed, then go for it.

I will tell you a way I have personally used which is the tidyest way I have found, but it is not the easiest. You will need a thin piece of wire, one that can go through the via that the track is connected to, and also sit under the IC without lifting it anywhere. Thread the wire through the via and solder it on the underside. Run the wire out to where the original pad was. Now place the IC on the pads and carefully lift the leg of the IC with tweezers. The rest of the IC should sit flush, allowing you to solder the legs to hold it in place. Once you have made sure that the other legs are soldered, and your bit of wire is not shorted to any other legs, cut the wire to length, and solder it to the IC pin. You can either leave it like that, or carefully bend the pin back down so it looks flush. This should give a good solid connection, but remember that depending on what the IC does, and what that track is for, it may no longer perform to the standards it was specified to.

Good luck!