First of all, thanks a lot for the code suggestion: It worked like a charm and now the EZ Bounce header is fully functionally in the bounced messages.
One more thing: Maybe the coder of this plugin can add an option to activate EZ Bounce header support, so we don't have to manually edit the product each time it's updated.
Unless, of course, he comes up with a better idea -- and I still have hopes for that.
Peace,
Gene