I am not sure if I am missing something or if this functionality exists yet.

Try this:

1. Save a chain of edges in a selection set

2. Save another chain of edges in another selection set

3. Start a Boundary feature.

4. Call the Selection Manager

5. Try to use the edges in the selection sets while the Selection Manager is on

In SW 2015 SP 4.0, it seems like the Selection Manager stays on, but the Boundary feature sees those edges individually.

Am I missing something?