How to get measure groups from Excel Pivot Table?

Question

I have an OLAP pivot table in Excel and I'd like to get the list of measure groups (in the Pivot Table Field List, these are the things with the large summation symbol next to them).

I'm using VSTO and Excel 2007 for this. I would have thought they'd be listed under PivotTable.CubeFields. This list does contain the actual measures, it does not appear to contain the measure groups. I thought that the Parent property of a CubeField may hold the measure group, but I can't glean any useful information out of the Parent property of the CubeField (it looks like an opaque COM object).

I could use ADOMD and hit the OLAP server to get this information, but I'd really like to avoid doing that. I want to do it by querying the Excel object model. I know that Excel has the information, as they display it in the Pivot Table Field List.