What I did was this, which actually works kinda brilliantly, to my surprise:
Open Keyboard Shortcuts app and add two custom shortcuts:
Name: Volume Up (via amixer)
Command: amixer -q sset Master 3%+
Name: Volume Down (via amixer)
Command: amixer -q sset Master 3%-
I associate Volume Up with F3 and Volume Down with F2 personally (because these are the keys on my laptop that have those emblems), but of course it’s up to you which keys to use.