Umm... I have a 2.8F 12/24, and the way I always used 220 film was to shoot the first 12 frames with the switch on 12, then after firing the 12th shot and before advancing the film, flip the switch to 24, which resets the frame counter. Then advance the film to 1 and shoot the other 12.
The big problem with this camera (other than the general hassle of using the switch) is that if you accidently flip the switch -even partway- the frame counter resets in the middle of the roll (be it 120 or 220) and then you have lost count of where you are in the roll. You have to either guess how many frames you have left and risk being wrong and losing some at the end, or go ahead and reload early, wasting film. After this happened to me at an important shoot, I taped the damned switch on 12 with gaffer's tape!
Oh, and the other obvious problem: you have to keep an eagle eye on your frame counter, because if you advance the film after the 12th frame, you will continue to wind on until the end of the roll! Might as well shoot 120!