How do i hide a group footer if it's the only group?

I have a report that sub-totals on a group, then grand-totals at the
report footer. If there's only one group, the sub-total and grand
total are redundant, so I only want to show one of them. I know how to
count the groups, then hide the report footer if there's only one
group, but my problem is I want to hide the group footer (sub-total),
not the report footer (because the report footer references what the
grand total is for, which is always necessary, while the group footer
references the sub-category that the sub-total is for, which isn't
necessary if there's only one sub-category).

The standard solution of getting a running count doesn't work, because
by the time it has reached the first group footer, the count is still
"1", since it hasn't gotten to the second group yet. The end result is
the group footer is shown from the 2nd group and on, but the first
group gets omitted.

Any ideas?

Thanks!