I too am somewhat confused by the question; perhaps a little more information is needed? However, I agree with KorpDeath - if DHCP is enabled, then he'll recieve an IP address when he logs on, at either location and you want have to much to worry about. The idea of two network cards isn't bad either, one for the two locations.

The main reason to use a VPN connection is to enable a machine to create a tunnel to another network. But from our understanding of the question, your asking what's the easiest way to setup his laptop to recieve internet service from home and work without changing much. Right? If so, VPN wouldn't have anything to do with it.