My question to you is how are you able to possess code subject to the GPL yet deny your employees access to the source code?
This is just a thought, and IANAL so I could be completely wrong here.
What if the organization, eg CorpInc, took software released under the GPL and made modifications to it. Then they installed the modified versions to their own computers. The modified version is clearly under the GPL, because it is a derivative work. However is CorpInc required to give it's employees that use those computers the source to the modified version? If they are, then by the terms of the GPL the employees can give the source, and binaries, to others.