|The problem is, if you have two separate routers configured for separate subnets, then how do you tell the traffic from the laptop to go to a certain router?|
Normally, your NIC get's assigned a "default gateway" IP address which in the case of a SOHO router, will be the LAN IP of the router. If you have two NIC's plugged into two separate routers configured for different subnets, you'll have two separate gateways and no way to tell the outgoing packets which one to choose. Your computer's operating system is not setup to do this
If both routers were configured for the same subnet you could maybe do this but, then the point becomes moot as in the end, the traffic is going out one gateway after all. You can't have two identical (duplicate) IP's on the same network. So you'd have to have the second router pointing at the first as it's gateway and assign it a valid IP (not already in use) in the same subnet.
What exactly is it you're trying to achieve?
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.