I don't know for certain about how the twin engine program on the jr9303 works but I just purchased a FrSky Taranis that uses OpenTX for the program and you can program anything you want in it. I didn't think about it until you just asked this question, but you could put both throttles servos on different channels and set each one up for a different curve and/or rate. In essence if the geometery wasn't perfect between the two throttle servo connections, you could correct for it in the programing of the radio. It would take a bit of trial and error but could be done with my Taranis. I just got the Taranis and am still learning all the things that are possible to program into it. I just got my flaps to go down at slow speed. That was cool.