Constrain bounciness in Y axis

I've got a game where you control a puck-like object and try to knock into your opponents to bounce them off the platform. I've hardcoded my own knockback collisions, also with a bounciness of 0.3 on the physics material, and that works fine. But the raw built-in physics when I set bounciness to max is what really gives me the game feel I'm looking for.

The problem is, there's also occasional vertical "jump" movement in this game. With max bounciness, the pucks also bounce vertically, which I don't want. I only want bouncing to happen on the XZ plane.

Is there any way to constrain or cancel-out bounciness on the Y axis?