I tried the shirt collar idea a while ago and found that my shirt collar would rub the mics more then when I had them on my shoulders.I didnt have it tight (the collar I mean) so it wasnt that. Also, for the record, I was being ballsy and ran an inverted DIN config (instead of pointing outward, they pointed inward) and the tape turned out great except for the noise produced by the shirt. So the mics could hide further in my collar then sitting on top of them pointed outward.
I do recomend using a dark color shirt, that matches the mic colors, and if you do use the hat idea (which I have no experience in, all my hats do not yeild well to puting mics in them... stupid fedoras) then get some dark croakies to attach to you (if you dont wear any, fake) glasses. Works like a charm. Also beware, that some people might hassle you for wearin a hat through a performance. Dunno the crowd at a Furtado show so you're in the know on that one better then I am, but I saw it happen at a BB King show I went to.
Good luck.
-- Page
PS: Is DIN naturally pointed outward or inward? I get confused sometimes. I know that ORTF is outward, and XY is rather irrelevent since they are right there, but I forget with DIN.