Years ago we made a servo operated kill switch, it has nothing to do with the choke at all. It was just a servo attached to a switch and the switch was attached to the ground strap. Today I still use an on off switch for my ignitions and nothing has changed, when on, it just grounds the plug/ignition like it always has. What the OP wants is to know how to make a kill switch operated by a servo. The servo arm just attachés to the switch arm. No mystery but it went out with bow ties and high button shoes. They tended to often create a RF problem that was hard to eliminate. Shazam, three decades later someone comes up with the same idea only does it electronically, calls it an optical kill switch and it's a new super duper item that you must have or your plane will fall out of the sky! Most the time I just use a manual switch. I have had a reason to have an optical on a plane once but that was it, once. I like the optical kill switch but it is not a must have item. For under 20 bucks they are cheaper then the switches I use so why not buy the optical.
To the OP. This is the beginners forum. Beginners tend to use glow or electric and not gas engines. When I have a question about any of my gas or glow engines I go into the gas or glow forum and ask my questions. I often find the answer just reading through the threads or doing a search.
The question about a servo operated kill switch is something I haven't heard even at the field during the BS sessions in the peanut gallery. Glad to see someone recalling the good old days. We have moved on from there though.