Bruce, Robert,
I agree that this could be done but that it is not worth the effort. If your users actually pay for your time, give them an estimate and ask if it is worthwhile. If they want to pay for it, go ahead. If you are a free resource to them, then don't bother asking and try to get out of satisfying the request. I like the solution of referring the user to Excel as an example of an accepted user interface. In my opinion, our job is not only to do what they ask, but also to help them decide what is worth doing in the first place.
HTH, Chaim