I haven't done it, but the concept is that you use PPM so you get 8 channels. Set up transmitter to allow use of all 8 channels. Do transmitter wizard and use all channels, including all accessory channels. If you are needing more than 8 channels, I don't know now to do it. I do recall seeing the 8 channel upped to 9 soon, but DR4 only does 8?
When done with tx wiz, go to Vehicle page and set "RC Input" Accessory 0,1,2,3 to output on your desired "RC Output" channel numbers.
Maybe fiddle a little on Output page.