I don't know if a channel expander can get you the functions you want. They are on/off or (on)/off. I know there is a switcher that can switch 6 or 8 channels between functions in a model. Like from drive to the rotator. You just have to leave a channel to do the switching. Lil' Giants Joe I am pretty sure has posted links to it before but I don't remember who made it. Easiest would be to just run 2 radios.
Might be cheaper too since alot of the fancy radios that have switch decoders cost $$