Filter on key figure structure

I have a BEx Query with a key figure structure in the columns, and I want to use a script (in a Button component) to switch between two of those key figures, while other key figures are also displayed. I got this running using a setFilter method with multiple filter values.

But, the problem is that this key figure structure has also some grouped key figures, and I don't want those sub-level key figures to be displayed. Also see the screenshot. So now if I filter on the MTD - '15 key figure, not only MTD - '15 is shown, but also the four key figures that are grouped below.

How can I only filter on the 'top-level' key figure? Exclusions don't seem to work.

Thanks,

Xavier