Unfortunately, there is no way to do this out of the box. You can use the Subtotal or Grand Total feature in the Grid and it will place a calculated member at the bottom that would return the same value as Month in your example. However, you do not have control over the label that it uses. In MDX, there is a function called Hierarchize that supports reversing the order so that the Parent is on the bottom of the list, but ProClarity does not use it. If you want to build a Named Set, here is the basic syntax:
HIERARCHIZE({<mdx set>}, POST)
If you build a set using this function though, be aware that ProClarity's Grid was designed to explicitly place the Parent item before the Children so you end up with a weird look to the indentation of the labels. You can get around it by using the Flatten Row Headers menu option, which removes all indentation.
If I knew of a way to post screenshots of all of this I would, but I'm not sure if TechNet allows it (I'm new to TechNet).
