Bridge tables and durable natural keys

Hi,
in the Data Warehouse Toolkit, Chapter 9, Figure 9.7 shows the Management Hierarchy Bridge table joining the Manager Dimension and the Employee Separation Fact table (using surrogate keys). A couple of paragraphs below this it states "You could use durable natural keys in the bridge table, instead of the employee keys which capture type 2 profile changes."

Can anyone clarify how this use of natural keys would be implemented - does this require the natural keys to be added to the Fact table as well (which is, generally, not a recommended practice) or, if not, how are the bridge table and fact table joined?

Thanks,
Nick