I would make a lever arrangement, as the actual movement of the choke mech is small compared with the pull of the choke knob, so just at one end of the lever have an eye(hole) that fits over/around the lug sticking out from the coke mech, other end of the lever is where cable attaches with solderless nipple(bike shop) then find a pivot point that is appropriate somewhere between the two.
Ie if the cable moves say 6cm and the choke mech pin moves 2cm that is a 6 to 2 or as it's better know a 3 to 1 ratio, now divide the arm/lever length by three and put the pivot point at the 1/3 distance from the choke end.
tabetha