I have run a roll of backing paper only without film through various 120 cameras, including a Bronica, to test the film advance and shutter. So yes if you hand spool 35mm film into the backing paper, it should work.
I think you could make the 120-35mm adapters work in a complex way on the Bronica EC by using the double exposure switch on the back. You would have to wind the film on the normal setting, guessing how many turns of the knob to advance one frame (you could measure this, but the number of turns will depend on how much film has been wound onto the takeup spool. Then, you push the back's double exposure switch to D for double, and wind again. This will cock the shutter without advancing the film. Take the picture, switch the back to A, and wind the film to the next frame, and so on.