EDIT: no longer works/works erratically, I have no idea how it works.
I find it a bit cumbersome to have to change the default button and then click "every time," and at the same time, I barely ever use the diagonals, so I thought it could be a good idea to have keypad keys 7, 5, and 9 set to the mouse buttons 2, 1, and 3 respectively (middle, left, and right, respectively). It partly deviates from the positioning on the mouse itself, but it feels more natural to have "5"...