L_ALT modifier + Scroll wheel

[scrymglin]

I've been trying to get a fairly simple re-mapping to work for days, and I can't work it out for the life of me.

I want to make 2 key remaps:
When I hold down L_ALT and mouse wheel scroll up, then generate Super_L+Alt_L+KEY_Up
When I hold down L_ALT and mouse wheel scroll down, then generate Super_L+Alt_L+KEY_Down

I just can't work out how to do it. I know it requires macros.

Thanks in advance