Pivot Table - Dynamic Dimension as header, depending on number of columns

[#1]

Hello,

I've got a pivot table with 15 formulas (each column filtered with set analysis). Now I want to create a dynamic dimension in which I write the values Day, Month and Year and put this dimension as Header above the 15 columns. Day should be centered above the first five columns, Month above the next five columns, and so on.

For example:

| Day | Month | Year |

| col1 | col2 | col3 | col4 | col5 | col6 | col7 | col8 | col9 |

Do you have an idea how to do this?