I already looked at

        http://boost.org/boost-build2/doc/html/bbv2/reference/generated_headers.html

but that didn’t help a lot, since the example it gives isn't very similar to my case.  What I ended up doing was putting these lines into the library Jamfile:

---

project workflow_mgr :

      usage-requirements <implicit-dependency>/workflow_mgr//Mock_workflow_mgr_core.hpp ;

mockgen workflow_mgr_core ;

---

The mockgen rule calls the make rule to generate header Mock_workflow_mgr_core.hpp from workflow_mgr_core.mockgen.