Just musing so to speak, as so far I have always stuck my wires into a straw, a posy pick or into a ball of gumpaste on the surface of the cake.
But.... Ron Ben Israel, in a class I took, said he puts wires directly into cakes and PinkZiab says at Pink Cake Box the wires are put directly into cakes, and Colette Peters, in her books, gives instructions for making decorations on wires and inserting them into cakes, so why are we (and I include myself) so paranoid when it comes to this topic?
It is likely that the artificial colors and flavors we use without thought could be potentially far more dangerous to more people than the small amount of lead possibly leaching into cake, but very few people are giving up artificial colors or flavors.
And yet,though I know a lot of people who are very sensitive to artificial colors, flavors, and preservatives in life changing ways (I'm related to some of them) I've NEVER met anyone who had lead poisoning--especially from wires in a cake. Can't quite figure out why we don't think twice about that artificial coffee creamer or all the little bottles of color, but we get crazy about wire (or a hair--which is icky, but not really dangerous.)
Like I said, just kind of thinking on it... Not going anywhere with it....