One trick is to use the throttle needle mixer. This mix was intended for mixture control with throttle but in reality it is just a parallel mixer. Like collective and trottle for a helicopter mix. use throttle for one engine and throttle needle for the other. Activate the mix and set values to give normal servo throw (I think default settings). Set each servo center and throw using ATV and Subtrim. Another trick is to use a product like the Matchbox by Jr. Futaba makes one too.

multiflyer