Fiori elements list report: Aggregate functions are not allowed in transactional views?

[M-A-R-C]

Hey fellow devs,

I am trying to show the total values in a grouped list in my fiori app. Basically something like this:

I have created a CDS entity, a projection (provider contract transactional_query) and a behavior. However it seems to be impossible to add a total value for a column. As soon as I add the annotation  @DefaultAggregation: #SUM to my CDS projection my service definition (both OData v2 and v4) will break and raise the following error message: Error related to element '...' of entity '...(CDS)': Aggregate functions are not allowed in transactional views.

So I am a little lost on how to add a total value to my list report. Does anyone know if and how this is possible or if there is a simple workaround?