Matrix subtotals, grand totals, selectable by the end-user

There are many similar suggestions, but this one is about giving options to the end-user. I have a matrix in a report where it is sometimes useful to have subtotals, and other times it is not, depending on how the Matrix is filtered. At the high level the subtotals are generally helpful, but when the report is filtered to a low level the subtotals add visual clutter. It would be helpful if the end-user could turn subtotals on or off, as is appropriate to what they are looking at. Basically there would be a way to make some properties of the matrix selectable at run time.