Over the weekend I was under the hood and revving the engine up by hand and I just happened to notice the rectangular cover plate of the MAF sensor moving out as the blower developed boost. So apparently boost pressure is able to reach the inner surface of the plate. It only moved about a millimeter or two, but it looks like the only thing keeping the cover from blowing off is the RTV type sealant around its perimeter. It's about 6 square inches of area, so at 9 psi there is ~50 lbs of force acting on it. This had me concerned.

So I got two 4" hose clamps and wrapped them around each end of the cover plate. No worries about a blown MAF sensor now. Ghetto, but effective.