Hiding group headers in a heirarchy while still showing sub-groups/detail

Hi,

I have a row group heirarchy a bit like this (the real thing is a lot more deeply nested):

Country
|
|--> State
       |
       |---> City

I'm trying to make it so I can conditionally hide a group header column showing, for example, states, but maintain the visibility of the City row headers and all the details. I'm not sure if I have the terminology right, but based upon a parameter, instead of showing this:

It should be possible to show this:

Make the grouping conditional seems to have no effect on the visibility of the "State" column even when the condition evaluates to Nothing. For normal columns I can right-click on the gray column header thing at the top of the tablix and click on Column Visibility, but that item is grayed out for row header columns. Setting the tablix member's "Hidden" property to true hides all the sub-groups and details, which I don't want.

Is there any way to achieve this?

Thanks in advance for any help.