toprudder,

I actually did this using the DX6 radio system -fairly simple. You remove the rx from the 4in1, using sidecutters you remove the plastic casing that the rx mounted in- leaving the new 3in1. You buy 2 each 3" JR servo extensions (1 end male 1 end female) then remove the outer sheilding plastic from the male connectors (so they fit in the female conectors side-by-side) and plug into the 4in1 ( channel 3 and 4 for throttle and rudder so 3in1 can mix with gyro, etc). Thiat is it. It works great! The DX6 rx is 7 gms but nice and small sized- just stickypad to the side and wire up L0)

Good luck!