There probably is a way tos et it up so that you do not have to save out seperate scene files but you will have to render more than one pass to do this without some hardcore plugin programming. It sounds like you want to control the visibility of an object not globally which you can do but per each reflective object.. much like the lights can be assigned to specific objects.
Anyway it may be possible to use a prerender MEL script that hides and shows the objects that you want reflected in each pass.
Take a look at the hide till render partition script here on highend in the MEL rendering section.
If you were to try to do this with rener layers you find that you would have to copy the same geometry to several render layers since a shape can onlyu be in one layerat a time. But perhaps the premelscript could move the common geometry for you.
Let's say you have three mirrors and each needs to reflect the same bakground but in each a different object.
You might make one render layer that has the all the background geometry and then three layers with the three different reflected objects and the in each the mirror that they are to be reflected in. The script would copy the background in to each layer before render time but only as reflected objects not rendered. You'll have allready rendered them in the background pass. The result would be a background apss and then three mirror passes each with a different reflected object.
To be honest I'm not sure what would be more work.. figuring out this script or just saving out the seperate scene files. If the scene file is huge and you'll be working with for a lwhile then it would be worth it to get this script to work.
