2d/3d billboarding in nearly top-down perspective

I have a billboard shader for a game with 3D environments and 2D characters. My question is if there is a way I can (via depth or timing) cull the sprite as if it were upright so it doesn't clip through geometry but can still go behind it.

I'd rather not cheat colliders so things can maintain a normal(ish) 3D space. Due to the severity of the camera angle, there would be a LOT of cheating

Thanks in advance!