if your using a y harness your not going to be able to mix anything. As stated the flaperon are only useful on full length strip ailerons. Even then it really a look what I can do set-up, only real advantage I've experienced is really tight loops which isn't something a warbird should be going. you'll be limiting the aileron travel and risking tip stall. Just leave it how it is and fly it.

If your stuck on using flaps do some kit bashing and put seperate flaps on. It's a real bear to do on a finsihed model