I'm pretty sure You just need to do another mix "elevator/flap mix",, the radio will account for the fact you're mixing ailerons/elevator also.

I had 3 mixes running on my Kingfisher to get the ailerons to drop with the flaps, I turned it off because the ailerons was too mushy on landing/takeoff, But Oh how it slowed down
If I remember right I had (1/7 Ail-Diff), (1/flap), (7/flap) I'm pretty sure You can mix as many things as you want and the radio allows


p.s.
Then mix the throttles with the rudder for variable thrust taxing