I just had a second thought. Instead of promising to be there, Harry should have gone to his Aunt and Uncle, gotten them to write a letter to the headmaster of Xaiver saying they did NOT give permission to go to Hogwarts, and try to get Dumbledore arrested by the muggle police for fraud. Then Harry could go there, and Dumbledore would have been disappointed on Sept 1st. No doubt he would try a kidnapping or something, but Harry should have made the attempt. Not to mention the inconvinence of the fraud and kidnapping charages.