You can use pass contribution maps with your re-combination. In this example, there is a pass contribution map associated with the masterLayer. This pass contribution map contains the reflective objects in the model: the helmet and the metallic tubes.

To create a Reflection pass for the pass contribution map and add it to the re-combination
to associate the Reflection pass with the pass contribution map. 
to render the Reflection pass.

.
The Render Target renders as follows.


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