How to make a material billing relevant - but not stock relevant?

Hi,

For my client I need to have a (A) service material that is pricing (optional) relevant - but not stock relevant / non shipable

It will be a line item along with another (B) physical product (which will be billing and stock relevant)

Both products A and B will be billed based on Sales order --> Delivery --> PGI --> Billing

The questions is : how is a material made non-stock relevant (so no stock is checked at delivery creation) ? a
What configuration is required for making billable but not ship-able?

Thanks,

SM