It's not ideal to send all stock requirements to the Back Order Control Centre, as the purpoise of the centre is to produce invoices. Service Manager has its own billing system separate from the Back Order Control Centre, so doesn't need a second one.
If you want to flag stock on jobs as required, you need to specify the required quantity in the Required field when entering parts/materials.
You also have to go into the Customize area and ensure that under Install Settings|Service Manager, General Properties, you have ticked Reorder Required Quantities.
If you do that, then required quantities on job cards are included as part of the total required stock, when you generate Automatic Orders (Stock Replenishment).