You can use a technique called "versioning" to handle this. Load everything you need from both sources, and mark all rows with a flag or indicator that identifies the data source. Also add this indicator to all composite keys.
Add a listbox to your dashboard with "Always one selected" enabled. You can create buttons to make selections in this listbox if you want to.
Later on, you can define common dimension tables that should be loaded only once and whopse rows applie to both "versions".
