I just can't do it. I tried, I really did. But W just begs to go forward.
Actually, the big problem is muscle memory in my fingers. When I anchor turn, I have learned to hit S and then Z really quickly. It'd be damn near impossible to unlearn that. At least more difficulty than I want to deal with. I guess I'll have to learn to by my own INI ninja. Or maybe someone at another forum has figured it out. Maybe starport?
Use X to anchor turn. Saves you time, anyway. W/S is much more useful as up/down than forward/stop. If you have to relearn your controls, fine. Just force yourself to do it for a day or two and ... you'll learn them.
Virus is right. I use Ctrl+W and Ctrl+S for fine acceleration / deceleration, because the mouse wheel only changes velocity in steps of 15 on my computer (mousewheel set to scroll 3 rows).
I've done the controls addon for 4.85 so I went over the files numerous times.
For me, there's no known reference to any key code that would refer to the mouse wheel, so I assume it's hardcoded in the binary.