Custom Grouping in a tabular model

Hi all,

Today we have a non tabular cube that we analyze by creating custom groups inside of an excel pivot. For example, using the current period (YYYYMM), we look at financial activity for a current period (ex: 202311), all prior months (202310 and before) and future activity (202312 forward). I do this by selecting the prior months in the pivot row and create a custom grouping in excel. I do the same for future months such that I end up with 3 rows - Prior Months, Month of Analysis, Future Months. This isn't elegant, in that next month I have to unselect and reselect in the pivot when I want to look at a different month, but it generally works well.

Since I can't use custom groups in excel in a tabular model, how would you implement this? The month of analysis is dynamic, in that I could be looking at August and want to display Pre and Post August as custom groupings. Has anyone had a similar use case with a tabular model?

Thanks!