You can bind whichever key you want via the default key bindings interface. Just drag the macro you created on an action bar slot, and bind that slot to for example "Mouse Scroll down".
The only problem with this (without use of an addon) is that if you bind a heal for example to Right and/or Left mouse click (which by default is interaction/attack with NPCs players) those bindings will disappear and you will have to set new ones for those functions (I usually replace them with CTR+Right Click and CTR+Left Click).
I hope this answers your question and that I haven't missed the point