I have a Fibrament stone and I have read the FAQ on aluminum foil that you mentioned. As you may have noted, the question on using aluminum foil was raised in the context of not wanting to stain the stone. The answer talked about the possibility of thermal shock, but my view is that if the stone can't handle a normal (or even wet) pizza dough--which is the purpose of the stone in the first place--it can't be much of a stone. We know for a fact that the stone can handle pizza dough, whether it is on aluminum foil or not. Maybe if someone put a frozen pizza directly on a very hot stone there could be an issue of thermal shock, but even there I am not entirely convinced. However, I don't plan to test the theory.
There is nothing wrong per se with using a sheet of aluminum foil. It's not much different than using an aluminum pizza pan except that it is much thinner. But, as thin as it is, the aluminum foil will still provide some thermal "drag" because, like an aluminum pizza pan, it has to heat up before the pizza can bake and the bottom of the crust starts to brown. If you wish to use the aluminum foil, for the reason you mentioned, I would wait until the pizza sets up and is rigid and then remove the aluminum foil so that the pizza can get decent bottom crust browning by virtue of being in direct contact with the very hot stone. The negative to doing this is that you have to open the oven door, which will cause you to lose oven heat. So, I would do it as fast as possible. Maybe you can try it out and let us know what the results are.