If you use Dimensionality() -- or SecondaryDimensionality() for rows -- you can create a custom total expression which you could use for your KPI value.
Set up a pivot table with Month as the dimension and Sum(Actuals) as the expression. Enable partial totals for the expressions (on the Presentation tab) and pivot the table so the Months are columns. Now modify the expression:
=If(SecondaryDimensionality() = 0, Sum(KPI), Sum(Actuals))
Finally, change the "Label for Totals" to read "KPI Target" (or whatever you want it to read).
If done correctly, that should result in the monthly amounts and the KPI value in the 'total' column labelled with the label you entered.