I meant to reply to this yesterday but forgot. I haven't done a true RBBC in a few years but I think most of what I did still applies.
You basically have two options. If u select your own offensive plays then they should still have the option to swap your HB when ever u want.
If u like to do the suggested play option u can formation sub your other HB in on certain packages and it will apply for the rest of the game. The down side is u have to manually do it while the play clock is running and it is a pain. It used to take me about 3-4 plays to get everything situated.
Those are the best methods I know. Again this is what I did a few years ago, and while I'm pretty sure it works the same, I'm not 100%. Hope it helps though.
Sent from my Galaxy s4 so deal with the short hand