Are you referring to computer control or piping the display of the 1200 to a monitor. Two different things. If you're looking for control, there are a host of options available. I like Log4OM, which allows me to "point and click" to navigate to a DX station via the cluster. Once I've made the contact I simply click the add button through the logging program and I'm done.
Ham Radio Deluxe is something of a replacement for the physical controls of the radio in which you can control most if not all facets of the radio via the program. You can still find the free version if you search. It's bloated in my opinion.
I used to use an RS232 to USB along with Omnirig for computer control. Make sure you get the FTDI chipset.
If you're looking to extend the TFT display of your 1200 to a monitor, the capacity to do such a thing simply isn't available for that radio regardless if you make some type of gizmo as an intermediary between the radio and the monitor, there is nothing that would allow you to project the display from the radio to the monitor. Each jack and/or input on the back of the 1200 has a specific function - none of which involves video.