To ignore on hand quantity for certain material (Low cost Items)

Clients are using low cost items, which are part of the BOM. These material are considered at the time of work order execution and expect them to get charged and cost roll up.

For which we thought for opting for supply type: BULK, where it ignores the material on-hand during the time of work order execution and also we have to report them manually. But when it comes to reporting manually, then if the quantity is not present in the supply sub-inventory then the transaction is failing.

Note: we are not allowed to have Negative on-hand balances.

Is there any other way which can be recommended to solve this issue. please suggest!