If you can't dim it electronically, how about putting a thin layer of tinted plastic over the display? Kind of like sunglasses for the display! You might even be able to find some of the klingy stuff, like the plastic that comes on displays to protect them. I've even seen tinted saran sandwich wrap in the stores. Or regular tinted plastic, and just put a tiny dab of rubber cement on each end to secure it, yet make it easy to remove.