sling aiming system would probably work like typical golf swing controls.
but with a smaller sweet spot and faster moving pointer.
So you'd need to hit the buttong faster and with more accuracy.
So typically you have a pointer or bar going round a dial, you hit the button once to determine power, and a second time for accuracy.
Unless you have a contrroller system like the wii, when you just swing like you're holding a golf club.
I like computer golf games
The same system would work well for slings.
Shame the wii is old now, but you could do the same with the switch controllers I reckon.