Mounting a camera to a camera

Why did I post about doing heavy multicam work in Final Cut last night?
Because this is what I did:

With the upper camera on full-auto with a 14mm (x1.86 crop at 16:9) I operated the lower camera on full manual to get some great closeups and medium shots.The upper camera gave me a wide shot of the same scene. The slight movement of the lower camera to frame the detail I want to show isn't noticable in the far wider shot of the upper camera.

This way in editing the video I can now show the closeup of insecure, shaky feet on a tightrope. Then cut to the wide shot to show that this is happening at the equivalent of a third floor between 2 tall trees. Then cut to the concentrated and freightened face of the person because in between I turned the rig ever so slightly.