MDX TopPercent across different attributes of same Dimension

Hi,

I have a simple Dimension that has the following format:

You can imagine that there are a few hundred codes looked after per agent but this is just for illustration purposes. As you can see, in most cases there is no overlap in the Branch to Agent, apart from a few cases where we have the same agent at different branches (Agent1).

What I would like to be able to do is get the aggregate of the Top N percent of each branch/Agent combination underlying Codes giving something like this:

Any suggestions are appreciated.

MrHH