Set Message Feed Between Pages

I would like to spin up a Message Feed between user groups. As such, I have two separate feeds set up on two separate pages. One's data source is "UserUnitsDS" and the other is "UsrTenantDS."  

Intuitively, I would like to set the Data source on the Tenant Page to UserUnitsDS so that they are both mapped to the same feed. However, that data source is not available from the Tenant Page.

What is the workaround for this?