How to pan AND zoom with the mouse?

[Stef1786]

When viewing fullscreen, I want to
1) Advance to the next/prev pic with the mouse buttons - this works nicely
2) Zoom with the mouse wheel - this works nice too
3) Pan (move image left/right/up/down) with the left button held down if the image is zoomed larger than the screen

I cannot get 3) to work. As soon as I release the mouse button it falls back to function 1)

Is there a way to override/ expand the commands of Options > General > Keyboard/Mouse?
Maybe with entries in keyboard.txt? To assign, say, Ctrl+Mousebuttons to navigate prev/next, or Alt+Mousebuttons?