Given that you can hire all the contractors you like... couldn't you just set up an external NGO consulting agency, which you contract work out to, and which has a "deal" to provide their employees insurance/benefits/pensions through you equivalent to what you'd provide—and then making your "hiring" process into a "certification" process that gives people exactly the credential said NGO cares about?

In other words, why not do what the military does, and branch off a civilian subcontractor?