I think OP would like to have a mask RE which just masks all instances of a specific object "automatically". Without the need of adding it manually to the selection. You can either use Object Gbuffer ID for doing so (clones inherit the ID) or use this "trick":
- create a dummy
- link the object to the dummy
- put the dummy into "Manual selection" of the render element
The mask RE creates a mask for the entire hierarchy, so also for the object linked to the dummy. Now when cloning the object, the mask "updates" itself because the cloned object is also a child of the dummy (note that you have to restart IR to see the effect).
Good Luck