How to add custom fields RTC model?

We are working on a RTC solution for the first time, now we have created the CompositeProvider to integrate (as Union) the VirtualProvider and the views that result of the RTC model creation and we are getting data, however, we just received a request from our client to include two custom fields to the model, these two fields should be populated by a specific business rule derived from Cost Center and Profit Center.

How can we implement this request?

We try to add these fields as attributes but it doesn´t worked for the data from the views.

We try also to create an additional HANA view with the specific data we need to integrate but it wasn´t possible to include it to the Composite as a join because the VirtualProvider in the CP doesn't allow it.

Finally, we try to add them as fields in the foundation view but we get an error message related to not having the same structure in ACDOCC.

What options do we have? Is it to modify the ACDOCC structure (SAP Note 2490888) the only one?