Assuming your server is also at home, what will happen is:

    Computer A > router > local server > router > Computer B.

Instead of:

    Computer A > router > Computer B

You can use some scripting and configuration to get the second one if at home. But basically you have to have a way to guarantee that both devices are at home.

To make sure both devices are home, you can assign static IP at the router level to the devices.

Now, if both devices are wireless.

    – Check you are home by checking the SSID you are connected to.
        – If you are home, ping the other device static ip.
            – If it responds, you can connect directly to it

If any of these fail, connect to example.com.