Alright, so if it affects iron salts and proteins alike, it sounds like a faulty enzyme (if not that, it's some other "iron from food to iron for blood" conversion problem), and I can see how the IV iron could be dangerous (since all humans are pretty sensitive to iron overloads).
Just as another idea, I wonder if you could more effectively absorb iron through the mucuos membranes (gums, nose, etc.) than through the skin, and if a carrier compound like dimethyl sulfoxide could increase the absorption through the skin.
On a side note, while looking for more info about DMSO, I found an odd article. Apparently it's is already used as a carrier for iron, but for plants. Weird stuff.