Possible ideas for "beam cut-off"*:

-B&M uses 'glare guards' on some of their lights- just make a longer version of that, sort of like how a visor or the bill of a hat cuts down on the sun's glare. Possibly make the underside (closest to beam) reflective to redirect light back towards the ground.
-Possibly use some sort of black-out tape at the top edge of a normal lens or just have like some plastic flashing extend down before the lens is installed.**

*Would work best with the so called 'dedicated' bike lights (like the NR MiNewt) that can only be mounted one way, as flashlights would be problematic to line up....

**Not responsible for damage caused by the spewage of beverages while reading this...