Screen protector will not actually reflect the heat a whole lot. I have had my Nexus 7 in 105 degree heat before and never had a problem with it, but I suppose if yours is having a problem you could buy a heat sink fan like you would use on a computer (example...http://www.newegg.com/Product/Product.aspx?Item=N82E16835103065). I would mount this behind the tablet and fairly close to it so it's blowing directly on the back.
I am not sure if you did this, but I rearranged the insides of my Nexus 7 so I no longer have a back on it. If you were to get a fan, pulling off the back case would help air flow get to the tablet. My tablet below for reference...