If you use their Apple-branded case, the little rubber band that goes around the outside edge, does that fix the problem?
I took a ziploc bag folded in half (therefore 4-ply) and wrapped it around the metal, and no matter how hard I squeeze it or cover it, the signal doesn't drop below 5 bars.
With it on, the glass is separated from flat surfaces you set the phone on, and the phone looks less distinctive too (which can be a good thing).