How to map two mouse buttons at the same time?

I’d like to pan the view by holding down the left AND right mouse buttons at the same time.

How do I achieve this? I can’t see how it can be done with the current keymap UI…

What you could do is if you can remap mouse buttons, assign a keyboard button to one of the keys and use that button together with the mouse to get it to work. Perhaps you’ll have more luck using button 5/6/7, because I don’t know what those do?
Otherwise, I think you may have to use a script or some 3rd party software…