[dsr_]

I'm right handed, so I would pick the bottom left button as the scroll lock, with the top left button as 1, top right button as 2, and bottom right as 3.

"scroll button is also usually the middle button" -- these functions are completely separable in libinput.

[pronik]

Meaning you would be pressing LMB and RMB with your index finger, moving it from the trackpoint itself? I can imagine controlling the trackpoint with the middle finger and use the index and ring finger to press the buttons, but it's far away from the "original" way to do it.