Sharing a broadband connection?

Suppose my Win XP pc is connected to ADSL broadband. My wife buys a laptop and wishes to share the connection, but is not intrested in a home network. I know that each machine could be configured to this ISP, and could take turns at using the broadband service by simply disconnecting one from the modem, and connecting the other in its place. Is it possible to obtain an additional IP address from the ISP, so that the laptop, using a separate modem, could be used simultaneously, from a splitter in the ADSL copper line?