Exclude shared members in Planning Form

Content

Hi,

I'm designing a form that retrieves a list of accounts under a parent as rows. However, I want to exclude some of them. For this, I have created an alternate rollup to use to exclude the members from the primary rollup in the form design. However, it does not work. I don't want to select individual members from the primary hierarchy, so is there any way to do this?

I tried to use a substitution variable with multiple values but it seems the form does not accept that.

Thanks in advance