I was going to say that you could. Your CFII says instrument airplane, it doesn't specify single or multi, so you should be able to instruct in both, but I guess 61.195 proves me wrong.
So here is my question, I have heard of people getting their CFII as their initial instructor rating, so what can you do with that? It just says instrument airplane. I know people have done this, so you have to be able to do something with it.