Conditional formatting based on the Hidden property of a row group

I'm trying to format the background color of some cells/text boxes in a report based on the current Hidden (Visible? Toggle? I'm not sure the right term) property/status of a Row Group (or it could be some other object--e.g., text box--in the report).

I put a document with screenshots and annotations at http://www.christianbahnsen.com/ssrs_conditional_formatting.pdf

The document may help better explain what I'm trying to accomplish.

Essentially it boils down to being able to determine whether a given row group is visible/currently expanded or not, and doing the conditional formatting based on that visibility/toggle status.

When the user expands a row group, it seems like there has to be an event that fires and triggers a postback.  Perhaps I could run some code along with that event to accomplish my objective.

I'd posted on this topic in the MSDN SSRS forum, too.  The thread is at http://social.msdn.microsoft.com/Forums/en-US/sqlreportingservices/thread/d493862f-7dca-4b28-8b20-797a4f15886f

Thanks in advance for any help.

Christian Bahnsen