So what you really want to do is get one of those Ford Focus louver systems from a rear-end collision junk-yard Focus, and adapt it to the Mirage! You might only be able to use the actuator mechanism and then design your own louvers to fit the Mirage spaces.
In my own case, I'll just read along with interest but not actually be concerned about modifying our Mirage unless we see winter mpgs plummet more than I might expect. I also expect I'd go the tape route first.
If I were to go higher-tech than tape, a louver system, I could control with a lever or knob from the driver's seat would be very nice. Something as easy to use as the manual choke I had to install on my '64 Ford Galaxie 500 would do very nicely.