Leaving aside the question of whether it's legally possible, then...

Is there any possibility of simply being honest with your current employer, and saying that you have the opportunity to interview for the job of your dreams, and that it's too much to pass up? (But that if it's not offered to you, you're happy to sign your current contract?)

Maybe this is highly unrealistic, but then again it depends on the people you work for. (I work for the civil service now, where it's *understood* that people will job-hop, so no one takes it personally. I've even known supervisors who actually keep an eye open for better opportunities for the people under them!)