Report Builder 3.0 Sorting by Quantity of Row Groups

Data is as follows

Group 1         -> subgroup 1 -> rows of data

                          subgroup 2 -> rows of data

                          subgroup 3 -> rows of data

Group 2         -> subgroup 1 -> rows of data

                          subgroup 2 -> rows of data

In this case I would want Group 2 to come before Group 1, because it has 2 subgroups. I tried using CountRows to no avail. How would one do this in reportbuilder?

Thanks