Untested idea:

If you are on subscription, you can set a warehouse to Restricted.  Transfer your special stock to that warehouse, and set user permissions for your order / shipping entry staff to not allow that warehouse to be used on the SO / invoice, and not allow shipping quantity to exceed QoH.  The user to handle the transfers in / out of the restricted warehouse would need extra permission to do that.

Otherwise, you can put the whole SO on hold, remove permissions to invoice orders on hold, and set up a script to control who can take an SO off hold.