Disallow drillthrough on matrix row headers

Currently, when drilling through on a matrix, it is possible to right-click and drill through from any cell in a matrix. However, it may be that essential data as defined by the measures in the Matrix Values needs to be passed to the drill through report, or the drill through report won't make sense (for instance, a dynamic Year selection may be portrayed as the column headers for those Values). We would like to be able to disallow drill through on the row headers in a matrix, as drilling through on a row header cell will not be able to pass a single year as defined by the Values measure