I'd say, since you've tried the spiritual angle and been turned down, it won't fly if you come back and say, "Okay, how about if I teach this course about aikido, the physical and philosophical martial art?" They're onto you now.
I agree with you Mary.
My own approach would be to promote it as a mind / body co-ordination practice.
But once they are on to you, I don't think it matters any more.