What are the criteria you are using to suppress the detail records? Let's say your suppression criterion was:
{table.field} = 'A'
Then you could create a formula {@notsuppressed} like this:
if {table.field} <> 'A' then 1
Then suppress the group header with this:
sum({@notsuppresssed},{table.groupfield}) = 0
There might be a simpler way, but we'd have to know your suppression criteria.
-LB