I was wrong about Bone Select. Any method of using non-self-shadow (Bone Select, model panel, light screen with Self-Shadow off/mode1/mode2) lets it sometimes work, based on camera angle.

Testing with NormalDepth-Core.fxsub for automatic reloading: changing CullMode to CW (clockwise; effect uses NONE, normal is CCW) makes ground stop showing flowers. Curiously, with CW, flipping the ground by 180° makes flowers show up and they don't flicker with camera.