Consignment, A/P, creating bill on the vendor record

I am trying to take consignment from my vendors but am kind of stuck. Here is how I think a workflow could work with very little JS knowledge.  It looks like some people in the group have done this.

Here is what I am thinking

1. Create a check box field in my items titled "Consignment" yes/no
2. Enter Purchase Order with Consignment Item XYZ with Purchase Price like ordering any other items
3. Recieve Purchase Order so Inventory is tracked correctly
4. Leave the Purchase Order on Pending Billing

Sales Order process:

1. Enter Items on Sales Order
2. Fulfill the sales order
3. Use a script that when Item XYZ is fulfilled, the original Purchase Order  is billed for however many XYZ items were just shipped. (system would recognize which items are which based on the check box and search for open po with this item on it)