You can try this, I have and it appears to work well. I installed an attic fan in the garage, such that it sucks air from the garage and PRESSURIZES the attic to force hot air out all of the provided openings. I also installed screened openings in the garage door to provide a way to get air into the garage.
I have not seen or noticed any hot air getting into the house. The fan is on a thermostat, so it only runs as needed. It will also run after dark, until the attic is cooled.
And, yes, this breaks the "fire barrier" in the garage, but so does the attic ladder.
I also have an indoor/outdoor thermometer mounted in the garage and the attic, and I appear to get a 30 degree drop when the fan kicks on.
I hope this helps, please feel free to PM if you want to see this or get additional info.
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Pennsylvania, for 60+ years, most recently, Allentown, now TV. 
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