Greenster, you didn't get my point.
Forget AppGameKit for a second.
If you want your employer to publish the app you wrote under his own Apple account (not yours), you need to send them the source code. The employer will then compile the app in xcode, sign it, and upload it himself to teh app store. That is unless your employer gives you his own Apple developer id & password so you can log into his apple account, compile & sign the app in his name, and upload the app yourself. but I guess few employers would accept this option.
When you put AppGameKit back into the equation, your employer has to buy AppGameKit, but this is only needed for 1 time.
In your scenario, I think, things would get complicated as usually these employers have little or no idea of app development, they are just project managers with good contacts, so as soon as you start mentioning agk licences, they might get scared away!