You probably can't, though if the feature exists, it'd be in your router configuration.
I think what you want to do, though, is be able to access your host on your computer from outside of your network-- in other words, you want to forward the public port 80 to the private port 80 on your computer, 192.168.1.2.
Depending on your router, this can be done in a "(Port) Forwarding" or "Virtual Servers" section of your router configuration. Create a new entry with any name, public and private ports set to 80, private IP set to your computer's private IP (192.168.1.2 in your example), and TCP or "Both" as the protocol.
Now when someone types your public IP address (to see what this is, go to whatismyip.com) into their address bar, your router will forward this to port 80 on your computer.