How do I avoid update checks for third party software (cobook), dont want to "update" by mistake
The MAS receipt is designed just so you can't do that - otherwise you could hand the app to all your friends without them having to buy it ;-)

Did you try telling App Store to "Ignore Updates" - right click in empty space to the right of the App name… though I've heard reports this is no longer working in Yosemite; I've no updates to test on right now.