A magnet is a good idea. However, magnets do not stick around the chute (or to the Mazzer shell). Attaching a magnet around the chute, with a matching magnet on the funnel, might work.
Why not just insert two M4's into doser attachment holes half way. Then cut two keyhole slots on the funnel. Then you just slide it in and out of place..
May you be cursed with enthusiasm for products manufactured in "developed" countries.