Shared data source connection (live to Tabular SSAS) for reports published on Power BI Report Server

I have just implemented PBIRS Aug 2017 Preview along with the Desktop RS (June 2017) app. I have a PBIX with live query against an SSAS cube data source. My report security on the server and against SSAS is set up to use a tunnel account, which means specifying specific credentials for the report to run as at runtime. The current desktop app for RS does not allow specifying a shared data source OR specifying credentials. Every time I deploy a change to the report (Save As to the report server), the server-side report's embedded data source settings are overwritten. Once I have both TEST and PROD set up with PBIRS, this will be a very brittle and time-consuming situation as I will have to update the data source settings with every deployment no matter how small the change was. PLEASE add support for both shared data sources for PBIX reports under report server and specifying the data source and/or credentials in the desktop RS app as a priority. This should work just like SSRS report development using Visual Studio, with an IDE connection, a published shared data source which is not overwritten with each report deployment, and the ability to create and use a shared data source on the server.