I don't think you are correct lore-wise regarding the inability of people (ESPECIALLY (half)-elves/drow) to discern between drow and half-drow. E.g. half-drows can grow facial hair.
If anything, they should have a few half-drow-specific options thrown. Right now, I don't think the game discerns between any subraces except Lolth-sworn vs Seldarine drow (which might be handled through the deity, not subrace, in engine).