Are you only missing the cable? Are all the pieces on the choke plunger still there, like the fork levers, springs, and little metal bar between the two carbs. If so, then maybe you can just manually push the plunger lever out and in. I think you can see and reach the choke lever plunger on the left side by the petcock. It might take a little bit of pressure, but you should be able to push it in and out with your finger or a hard piece of metal like a key. Or you can weld or install a metal stick in there and pull the stick for easier use.
Don't take my word for it. I'm just a foolish newbie.
When in doubt, just know that I am only joking around.
Top speed is 112 mph at ~7900 rpm
Blacked out engine
Dry rusty splines finally lubed for the first time
R/R relocated to the side of fuse box
Rust removed from tank
In line fuel filter, 23-28 micron rating
LED turn signals & brake light
16 color LED engine light up & underglow