Well, a large number of the pins are just ground pins, so the loss of a couple may not even affect the chip at all.
I believe some people have found sticking pins into the socket, at the spots where the pins are missing is actually good enough, as when you install the chip the pressure of the heatsink will be enough to make a working connection.
It may be possible to solder on new pins, but I'd have thought that even a really good job would risk heat damage to the cpu. Never tried it myself.
Probably worth trying the pins into the socket technique, as if it doesnt work, you can take them out again, it wont harm the motherboard. Just make sure they are not too long (or two short), they need to be just the right length to make good contact with the chip, without lifting it out of the socket).
If it doesnt work, you can still buy a new cpu later.