I'm sure it is possible, but in the time it would take me to do it could earn far in excess of the cost of a new router with a simple web interface that he could actually use to swap account detail

If I remember rightly my Dad's Zyxel also has a CLI, but you can't access any of the ADSL or firewall settings from it, doh !

He could do with a new router anyway. He currently has a router, hub and WAP, the last two of which he only actually needs when we go to visit.