Set Combined Nominal Budgets as not available for purchasing

I would like the ability to set up Combined Nominal Budgets with the ability to flag them as not to be used for purchasing. For example a budget that should only be used for staff costs I would like to not appear in the workspace for people to use when raising requisitions. We have had issues with departments with similar names being used incorrectly and now they have been used we can not remove the budget from the system.