Formula field, total percentage question

I currently have a formula field called %Total:

Sum ({@Total}, {@ClinicName}) % Sum ({@Total})

I would like to be able to show that all of the percentages shown in this formula field do, indeed, add up to %100 and show this in the Report Footer.

However, creating a summary or running total isn't available for this purpose.

Any other way I could do this?

Thanks.