Hmmm never been asked for this before - I would reverse the alignment but as you say stationing will be wrong but you maybe could get it into CAD via a pdf output and relabel the alignment - I cant think of a way other than maybe using station Equations possibly on a reversed alignment - but I dont think you can reverse stationing direction which is what you need to do
Let me think a little on this one - you come up with some real brain teasers up there in CA