Need to reference a concatenated footer in a report heading

I have a concatenated footer that takes each group heading and combines them all to one field. I found the formula on this site. I need to use this field in a heading but
I can't seem to get it working. The field is reset once I try to reference the field in the heading formula. I'm trying to get a heading that will reference each group in the heading. The groups will change based on a parameter. The 3 formulas to get the concatenated works great. For example

Group 1 A
Group 2 B
Group 3 C

Concatenated field formula becomes A / B / C (which now should become part of my heading field). Does anyone have any suggestions?

Thanks
Sandy