You would typically use a mixer to mix the elevator channel to another (unused) channel. Or you can use a Y-cable with a reverser.

The U-Can-Do has 6 servos so you should be able to program a mixer with your 6EXAS, i.e. just mix the elevator channel into the landing gear channel.

I have a Hitec Eclipse 7, and one of the drawbacks of that is that the trims do not affect mixers. I.e. if I mix the elevator channel into any unused channel, it works but the other elevator side does not move with the trim. I first tried a reversing Y-cable, but that was both temperature and battery voltage sensitive. I mean the center position of the reversed servo also depends on those, and it was a major pain. I finally solved the problem with a Schultze Alpha 8.35 receiver (don't know if they have a 72MHz version, mine is 35MHz), and programmed the mixer into the receiver.

The Saito FA-82a is a great engine, I have that one as well.