Remove-PowerBIWorkspaceUser for service principals and aad groups

Hi, 

I am currently developing a script for setting up customer workspaces. I make heavy use of the Power BI PowerShell cmdlets whereever possible - and if not REST-API. 

Addings members of type "App", "Group" and "ServicePrincipal"  with Add-PowerBIWorkspaceUser is supported. But the removal of "Group" and "ServicePrincipal" via Remove-PowerBIWorkspaceUser is not. I can also find not the correct REST-API endpoint. 

For each workspace permission role (Admin, Contributor, Member, Viewer) we are making use of AAD groups. ServicePrincipals are used to automate processes. The question is now: How to i remove those groups and principals once the assingment has changed via PowerShell?

Pretty sure its just me having to much tomato soup ...

Thank you very much

Greetings

chwolff