In my current XCF campaign, I carry a pistol just to shoot the Zzzz zombies on the ground.
I think the question could be re-phrased as, if there is a way to use melee weapons to finish off units on the ground, other than what was disabled a while ago.
My understanding is melee cannot attack terrain, like the Pickaxe does. The Kukri knife can chop weak terrain (like a real-life machete or real-life axe) and could be potentially used for this purpose of finishing off units.
A suggestion would be to implement this type of secondary attack to other suitable melee weapons.