Sort of did the same this evening. Along the Mount Vernon Trail there is a really dark area just south of the beltway. A commuter biker in front of me had panniers with reflective tape but no lights. It was well past dark at this point, so I trailed him and shined my headlight for the both of us for a little bit before I had to get to my turnoff. I hope he got home safe - the rest of the trail is awfully dark towards Mount Vernon.

Don't have Bi-Xenon HIDs, but they are steerable