although the set ups are different, maybe you could give it a try.
in about 2005, the ford taurus had a steel 16 inch steel rim with plastic hubcaps. we would get complaints of noise while driving...bumps, turns, etc. ford has a tsb out for this. the fix was to pull the hubcap and clean the outer edge with alcohol or an equivalent. our dealer has an "anti-rattle and squeak" kit, im sure they all do. all it was, was a small tackle box type thing filled with various size and density foam/rubber pieces with adhesive on one side. wed take 8 fairly dense pieces about half inch by an inch and space them evenly around the rim. re-install the hubcaps and ship it. took care of every car with no complaints....unless the surface wasnt clean enough and they fell off.
now, these were plastic full hubcaps that were attached with the plastic lug nut caps. i know its a different monster but maybe its worth a shot??

bob