They're actually already doing it. There was a story making the rounds recently about a couple of Ukrainians in an unarmed Yak-52 shooting down drones by just flying alongside it with the canopy open and the guy in the back seat leaning out to take the shot.
I saw that video and it was amazing. I'm trying to find it but can't.
Nevermind, found the yak video but it's just the pilot circling a drone with a deployed parachute. There is a video of Ukrainians in a Cessna-like plane shooting down a Russian ua with a rifle though and I still can't find it.