, many RC planes use the non-throttled versions of the Cox engines, although some use the throttle versions. Nothing prevents RC versions from being used for CL. I remember a friend flying a throttle controlled Testor .049 P-26. The third string had a line with a ring for the index finger. It was spring loaded, tugging on it changed the throttle.
I've never used an RC engine for CL, except for one which I wired to hold the throttle wide open. For RC, back in the 1980's I used a Cox .049 R/C Bee. It had an exhaust throttle muffler that worked very effectively on a Sterling Minnie Mambo single channel rudder plane with auxilliary sequential quick blip throttle (HI - MED - LO back to HI).
IMO smaller CL models don't really lend themselves well to throttle control, being marginally powered to begin with if a reed valve .049 is used, and especially if there is any breeze present. For me, simplicity is better. Plus, when one lowers the throttle setting, it is easy to lose line tension. On the larger jobs, like the .35's on up carrier models, they have articulated line leadout guide and rudder, so that when the throttle is chopped they cant the aircraft outward to maintain line tension.
Cox International http://coxengines.ca/
has both exhaust throttle rings for all Cox .049's and choke tube throttle for SureStart .049's, if one wants to experiment with throttle control. Given the low investment costs in 1/2-A CL, nothing prevents experimentation.