Its a technical draw and your opponent is obliged to accept the draw.
Stalemate is when your opponent can not legally move a piece. I
agree that they should have some sort of mechanism in place that
ends the game when the type of situation you described occurs. If
your opponent knows anything about chess he should accept your
offer of a draw anyway 🙂.
That is not needed in this case. Any game in which one side has only
the king and the other the king and a bishop or knight (or only the
king also), should automatically be a draw, because there is no
possibility of mate. So you don't need to play on for 50 moves. I don't
know if you can ask a moderator to manually declare the draw, but
that would also work. Also, if your opponent only has a king you can
demand the draw if you want. On yahoo, if you run out of time and
your opponent has only the king, it's a draw for instance