Lockout individual parts from being sold

We need a way for BW to acknowledge a minimum required on hand quantity level and backorder at that level (not zero). We have stocking levels set on all inventory parts. One item we sell all day long, is fuel filters. Our suppliers are having raw material issues and delivery time is months and months out. We are oversold on almost every sku. Customers buy them by the case. We ship most of our product out, but we also have a sales counter that accepts walk-ins, and we need a reserve level to be able to fulfill those walk-in customers.

We always want to accept backorders. We do NOT want to have to set up another warehouse. We just need BW to start backordering customers once we hit that required threshold instead of at zero quantity on hand. And we would love if the system would flag the line items when added to quotes and sales orders. Automatically backordering at a packing list level would be so beneficial. We are constantly having to override and modify packing lists currently, and some are getting missed.