A common solution is to engineer a tiny bit of play ( 0.020 - 0.050 ") into the linkage between the master and each individual throttle. That way, at idle, the individual adjustment screw controls that runner, allowing very fine adjustment. As the go-pedal is pushed, the master takes up the slack, and then controls all of them. Ideally, the play is equal for all, so that off-idle synch can be performed. But at WOT, they are all open fully against the stop anyway, and so any play becomes moot.
Carter