I haven't tried it yet, but I book marked this post for the same issue.
Yes, the normal way to do it is to mix two switches using the programming in your transmitter. If you have 2 2 position switches you can mix them to get 4 positions. If you have a 2 position and a 3 position you can mix them to get 6.
How you do it is dependant on what transmitter you have. On some it is quite apparent and easy. On others it is difficult. I have successfully gotten 6 positions on all of these radios: DX7, DX8, JR9303, JR7202 and TGY-9X. In short I have been able to figure out how to do it on every radio I have tried, although it was difficult on the TGY-9X. Of course the programming on that radio is generally cumbersome and the manual is useless.
You also can select flight modes using a knob or slider, but this is difficult. There is one user who modified a knob on his radio to have detents, but that was on a TGY-9X so I wouldn't recommend that as you can do it through programming without hacking the hardware. If you have a radio that just can't do it there is a thread on the site here describing how to hack a TX using a rotary switch. That would not be a bad way to go.
I am using an older 6 channel Futaba T6AS computer radio.
The radio is equipped with 1 rotary pot that is labeled FLTRM.
With proper programing the pot is slaved to channel 6.
From the way I understand it the flptrm pot would enable ailerons and flaps.(not combined like flaperons)
I am using the ailerons on channel 1 and APM mode selection on channel 6.
With this this simple configuration I am able to select 5 distinct positions via the rotary pot (9, 10:30, 12:00 1:30 and 3:00 o'clock positions) allowing for a choice of separate 5 APM modes.