How do I make a character step up or down with a NavMesh?

So I'm using the built-in navigation stuff that comes with Unity 3.5, and I'm trying to get a character to step from a lower mesh to a higher one. But when I bake the navigation mesh, it just slopes from the lower mesh to the higher one so instead of stepping up the character just gradually floats up to the higher mesh. Anybody point me in the right direction for resolving this?