When I program my own software I use a dual-J1962 breakout box and configure the two interfaces for different addresses. There's nothing fancy required, you can connect several interfaces to the network at one time with different addresses. Will your CarPC software offer this flexibility?
Unfortunately your two tools may be hardcoded to use the default tester address. In that case you would need a switch-box so they won't conflict by trying to answer on the same address at the same time. I've never seen a switch-box for sale; you may need to hack something together. You could build something completely custom with connectors from obd2cables.com. Another option is to modify a dual-J1962 box with a switch/relay on the network or power lines so only one tool is active at a time.