You cannot "steal the block". You must commit to the full solution (including who it pays) before testing it. The reason this doesn't prevent defection is that

You cannot "steal the block". You must commit to the full solution (including who it pays) before testing it. The reason this doesn't prevent defection is that while you can produce a provable commitment that you're mining with the ES miners in one moment, all other moments you can be defecting and sharing the ES state with your friends.