I believe this tannin leeching effect is caused by the complex mixture of albumins and globulins contained in egg whites. While whole grains such as wheat are a good source of these compounds as well, I'm not sure that it would have the same effect. I make this hypothesis because the egg white mixture is in complex with water and a small amount of fat, which may give the egg white some level of internal no pols solvency potential (again, I'm not certain, this is just a guess). I suppose it could just a matter of a permeable fluid surface which works by catching the undissolved tannins. Perhaps you could try using whole wheat flour, then filtering out of you mixture and pressing as much of the solution out of the resulting mass as possible.
I look forward to seeing how you go, no matter how you choose to go about it.
EDIT: first post in the nexus proper! Woot woot!