Merge Queries from different dataflows (PRO license)

Here is my use case.

I need to import Invoices from one system, on-premise SQL Server.

And Projects from another system, Azure SQL Database.

Since extracting from an on-premise SQL Server requires a gateway, I understand I have to create 2 different dataflows since there is a single gateway configuration per dataflow.

Then I need to merge the Invoice and Project table together, but since I don't have Premium license, i cannot use linked entities.  Is there anyway to merge tables from different dataflows  ?

Or I'm stuck having to duplicate the merge logic into each .pbix using Power BI Desktop ?