Sometimes you can get a pair of vice grips on them. Otherwise spot weld on regular nuts and spin them right off.
You can also check with the nissan dealer. They might be able to reference the VIN with which key was provided - most manufacturers only have 5 or so different lock keys. Problem may be that the lock kits come from the parts department not shipped with the car, or that's how mine was packaged anyways.
Did I mentioned weld a nut on?
