Pairing of central locking remotes

[PeeBee]

I had a remote central locking immobiliser installed when I bought the 97 GQ. I drowned it in the McAlister at Burgoynes at 20,000klm, and the electrical repairs were extensive. One item replaced was the remote/central locking module - aftermarket brand, no name, but they only coded one of the two push buttons. I stumbled across the second push button the other day, popped new batteries into it, but it does not egister, so suspect the frquency is different, however the fob push buttons are identical - pulled them both apart and they are the originals.

Is there a generic way of 'pairing' the fobs to the controller? I can't see any component on the board inside the fob, like dip switches to adjust. If it doesn't happen its not a biggie, just looking for some back up in case the fob goes missing and I get stranded with the vehicle immobilised.