Replacement for a trivial Autohotkey script

Question

This no-brainer has been running on my Windows systems since XP:

WheelUp::return
WheelDown::return
$NumpadSub::Send {WheelUp}
$NumpadAdd::Send {WheelDown}

Basically, it blocks the broken wheel of my ancient but otherwise serviceable mouse and allows me to use NumAdd and NumSub instead. What I tried to replace it on Ubuntu with:

1. xbindkeys + xdotool. Mouse wheel blocking works but mouse wheel emulation does not: 'clicks' emulated by xdotool get blocked by xbindkeys too.
2. xmodmap. All kinds of weird side effects. People say it is deprecated and should not be used.
3. xinput. Does not work at all, supposedly because of a conflict with libevent. Removing the latter as advised on this site disabled my keyboard and mouse completely.
4. Took a look at xkb but could not find any actionable documentation.

Overall, I'm at a loss and thus request something like a solution. Ubuntu 18.04.3.