How can I trick Minecraft into thinking two computers are on the same wifi network?

Using Hamachi, here's how I solved the problem.

Briefly:

• Join a Hamachi Network on both computers
• Hit Open to LAN on one (the host)
• Join hamachi-ip:port in direct connect Minecraft option, where port is the port listed by the host Minecraft when you hit Open to LAN, and the IP is the Hamachi IP of the host device.

You need a VPN. Tunngle is a good solution for games if you can deal with the ads, otherwise use Hamachi if you're prepared for the possibility of having to deal with configuring adapter priority. Hamachi is a lot more friendly toward creating private networks, which is a plus if you don't want your server to be raided by strangers.

I haven't tried it yet but http://www.minecraftforum.net/topic/1448177-minecraft-open-to-internet-v05/ looks interesting.

One side would run this program, and give the other side its internet IP and the port number, and then the other side should be able to connect as if it was a normal server.