Same Parts; Different GSI requirements

As a prime, we use a sub's component on a number of long term projects. Some of the contracts invoke Government Source Inspection that flows down to this sub's components. Some of the prime contracts do not invoke GSI. It's not always the same project or the same Agency. Seems to be a coin toss. Other than outside source inspection, the parts are identical and have the same sub part number. Our drawings for the different projects call out the same part number as well. To order these parts under separate part numbers would be costly as the sub will not offer a bundled price without a single contractual document.

Without spending a lot of extra dollars that the Government refuses to pay (all FFP contracts) to create segregated inventory systems, what are the options? If we commingle the inventory under the same part number, do we violate the GSI requirements? Do we need to formally request the Government to invoke GSI on all projects so we can commingle parts whether they desire to or not?

Some sage insight would be appreciated.

Thanks