I don't use the silver magnets or trickle tanks, but I am considering them. Right now I take my chemicals to the local haz-mat disposal yard.
Perhaps if Kodak, Ilford, et al included silver magnets with their fixers along with rebate forms? Build the cost of silver into the product, but make it so the customer can get gift certificates or coupons when they send in the magnets. Something like the redemption value for bottles and cans is what I am thinking of. Not only does it reclaim silver, but it gives customers incentives to keep buying the company's products.
Have you tried pitching the silver magnet thing to Freestyle? Maybe they could serve as a sort of "collection center," and provide in-house coupons to those returning magnets. It would maybe be possible there, but likely not with Kodak or Ilford directly. I don't know if they would bother.