How much space between inner and outer roof?

[purple gas]

Is there any kind of a spring, or wire fastener that could be used? Maybe a piece of that real stiff wire they use for keeping body molding parts on could be suck in there with a bit hanging down to attatch to? Just brain storming,, would be better than poking holes in your roof. ( what can I say, I came from the farm. When you have a tough job to do you always wonder what item never intended for your situation could be made to work.)