I understand that it is not possible to zoom with the mouse wheel. You want to keep that for turning knobs.
However, why not zoom with the mouse and right mouse button? I had the same discussion with Laminar Research, and they never considered this option. I mean, it is quite simple: You look around with the right mouse button, you zoom with it. If you want to turn something you let the button go.
Moreover, I can set an axis for zooming in FS2. But it also does not zoom in the cockpit.