I'm thinking 2 cyclic servos - left / right mixed to rudder, up down mixed to elevator. 3rd servo collective mixed to throttle. Or go the CCPM (?) route with several (6-9?) mixes to link to the tail with some creative math that takes the 120 degree servo postition on cyclic / collective and translates to 90 degree offset on the tail. The simplest approach would be a traditional heli design rotor that uses a separate collective servo. So you'd have 90 degree offsets on the cyclic, which match the tail for simple mixing. Mixing can be switched on / off with switch for cyclic (off = neutral), separate on/off for collective mix to throttle (off = full forward) .. Make sense?