Diffusion of oxidized color developer is in a sphere around the site of development. The lifetime of the oxidized color developer is longer than the diffusion rate into or through more than one layer. Thus, all colors will remain contaminated.

The solution you suggest is therefore not viable. The correct solution is to add an oxidized developer scavenger to either the film or the color developer. Sulfite might work just fine, but it can vary in concentration due to aerial oxidation. Therefore it is best to add an antioxidant to the film, in the interlayers.

Any suggestions on modification now?