Update Power BI API to allow seting a Data Gateway Data Source as the data source on a paginated report

I am using the PowerBI API to push paginated (.rdl) reports to workspaces. I then want to update the report data source to map to the proper data source that already exists in our on premise data gateway.  The Update Datasources in Group API call currently does not accept a GatewayId or DatasourceId parameter and therefore can't set the report to use the proper data source.

I have submitted a support request and was informed that this functionality is not available yet.