Supporting a fan in second (fake) ceiling
I'm not sure how acceptable this is, but it should work.




Install a brace in the attic between two joists (metal or wood should work).
Do your best to drill a straight hole, right where you need it, up through the upper ceiling and the brace you put in place.
Install the ceiling box brace between the metal drywall supports.
Drill a hole through the brace and the junction box.
Install threaded rod, nuts and washers as specified in the image.
Attach the junction box to the to the threaded rod.


Getting this all lined up is going to be a bit of a challenge. You could drill a bit larger hole through the upper ceiling, to provide a bit of wiggle room. Just do your best to contain the dust, and make sure you wear a respirator. It's only going to be a little bit of asbestos, but it's still best to avoid breathing it.

The threaded rod should provide adequate support for the fan, and the brace should prevent any side to side movement introduced by the fan. You'll want to use a metal junction box, or any box that is designed to support a ceiling fan from a brace.

You might want to use some jam nuts and/or loctite, as well as bend over the top and bottom of the all thread or install cotter pins. Just so the vibrations don't loosen anything up, or cause the all thread to unthread. 

WARNING: This is a hairbrained idea that was conceived before my morning coffee. Proceed at your own risk.



Another option might be to install the junction box in the upper ceiling, then hang the fan down through the lower ceiling with a downrod. However, you'll have to find a way to mitigate any side to side motion caused by the fan. A rubber grommet in the hole in the lower ceiling might work.