>Garrett's workaround isn't clear enough for me to implement.

I think it's pretty clear

1) Create report variable
2) Store desired header info to it, resetting on group.
3) Edit header field to include IIF(EMPTY(reportVariable), fieldInfo, reportVariable)

What exactly is in your Group Header?

Create a variable from the Report/Variable menu, say, fixGroupHeader. Set the expression to "My Group Header " + GroupField, reset on group.