A simple answer would be to create a dummy dialup connection (set it up to dial your house, or 1-800-flowers or something). Then turn on ICS and set it to never dial a connection (turn off remote control of the connection and turn off automatic dailing).
You don't have to use the connection to have DHCP on. Just setup the connection and ICS and then DHCP will automatically start when the machine starts so that in the event you need it, it is ready.