Sales Cloud Reports - Anchor ID and BusinessPartnerInternalID

Hi,

I have as requirement to build a report gathering Data sources "Account Master Data" and a custom BO called "Diploma" built via SDK Cloud Application Studio, which are Diplomas attached to accounts basically.

However, I have created the ID Diploma_AssignedAccountID as "ID" element... now I can't build a report as "ID" and "BusinessPartnerInternalID" are not compatible for anchoring.

Do you happen to know how I can convert ID element to "BusinessPartnerInternalID", or any alternative solution?