So, you have an air-gapped pc, let's assume for either security, confidentiality, or both. But it has exposed USB ports. Seriously?
Ok, so let's assume you will be allowed and/or forced to use some USB storage, for say, backup storage, in case internal storage goes titsup, or because internal storage is read only and nobody wanted to put a secondary r/w medium in it. Whatever. Now you have transmission capabilities.
And all that security/confidentiality issues that lead to an air-gapped pc, didn't lead to a (modestly) secured space. So much so, a fellow bad person can be just in range to pick up said transmission.
And of course, you need someone else to plant the code for the tool that you'll use. Someone that has unchecked access and permissions to the box so he can just drop in a tool that will be allowed to run.
Interesting from an academic point of view, but if this gives you any loss of sleep, you are already doing it so wrong it will be the least of your problems.
Think i'll write a paper about using a large mallet and leaking data by bit banging it (literally) on the wall while someone else picks it up with a seismograph. Devs are known to be weirdos so pretty sure no one will question the odd behavior. Coat. Mallet. Door.