Hi, I think there are some easy ways to do this.
1. Use another Queue. Send all good Items to this Queue (and from there to the right Queues in Process) and all scrap Items to the other Queue. So your Processor only has 2 Ports and you can send stuff via "by Percentage".
2. Give your items another Type by percentage. So just say, 15% of all items get another Type (and define another Port By Case for this Type), the rest stays with the Type that is already set.
3. You could add a "Quality" label that has another value for all scrap items. Lets say Value 1 is scrap. Than you only have to make the red Queue PULL all Quality = 1 items. This way would become a little more difficult, because you will have to set all other Queues also to pull the item.Type you want in there. Send to Port by Case will not work as it does now.