Hey.
I see this has been viewed a few times, so I'll post what I ended up doing.
The issue totally revolved around the mdl being built from Contrib extension using external rollups.
ie. the numbers in the cube do not really roll up via calculation, but are provided by the Publish.
Because of ext rollups, I could not easily add the dimension.
But, because we were publishing lots of data at the detail level, I was able to find a solution.
I reconfgured all the original dimensions to NOT be external rollups, and also added my own dimension at that point, and manually created a cal hier for it to reference, and added that to the datasource.
huge pain in the ass, but all the numbers tied out at the end of the day.
morla of the story is that is is very difficult to manipulate contrib generated mdls becaus of hte external rollup feature. If I had any complex calcs involved in my rollups, I would not have been able to do this.
cheers.