i tried it tonight. put the baking stone on one side of the grate and started a really hot oak fire next to it, then tossed some of the burning chunks under the stone. used a simple dough recipe from the kid's cooking class, some jar sauce to be quick, fresh mozzarella, and whatever anyone wanted on theirs. it worked fantastically. i've cooked many other things in the fireplace, usually in a pinch when the grill is out of gas or when it's just too snowy out to deal with it, but this is the first pizza attempt. quick cooking time(10 minutes rotating for even cooking), crisp crust, slight smoky flavor, cooked all the way through.
the kids got to make their own small ones
next time i will get the fire going sooner, the first two took a little bit longer as the stone was not hot enough yet. i started it about 20 minutes prior to first cooking. the last one went one, got great crisp crust and cooked much faster, by then i had a heck of a fire going and lots of hot coals. you can see the size difference of the fire and coal base between the two pics, the bottom one was first and the heat source was smaller. all in all, i give it a great success and proof of concept. beats the hell out of 99% of the restaurant/carryout pizza i've had.