Semantic model refresh by guest user (API or schedule)

Thanks but that isn't the issue. 

We have a tenant, dataTenant.onmicrosoft.com.
I am a user in mainTenant, [email protected].
I am a guest in dataTenant.onmicrosoft.com
I have ownership of a BI workspace.
In a semantic model in that workspace, I save valid data source credentials using [email protected]
AN on-demand refresh works.
I set up a refresh scehdule, the scheduled refresh fails.

If I set up an additional user with similar access but as a member (not guest) of dataTenant.onmicrosoft.com, (e.g. [email protected]) and save the data source credentials using that user the refresh now works (without changing ownership of the workspace.

I hope that gives a clearer picture of the situation.

My thoughts on how to work around this:
We do have at least one user that can refresh the semantic model but had not intended to create multiple identities for users across different tenants, we wanted them to be able to use their existing account once they had been invited. 
I had thought that scheduling could be orchestrated elsewhere using API calls (which makes sense as it could be tagged on to the end of an existing pipeline meaning it was only refreshed when required) but it appears that a call to trigger an API refresh relies on the saved data source credentials (not the user authenticated to make the API call).  To make this work I think I need to be able to save valid data source credentials then trigger a refresh.

I hope that makes sense.