What about laying the ipad face down on an appropriately sized heat-pack? I'm talking about those grain filled things that people use for bad backs etc. It might take longer, but may be a bit safer too. Give it a bit more microwave juice than you would for application to skin, and maybe some pressure and it would be approaching the right temp surely. I've never had a bad back, or broken ipad so I'm no expert, worth a try though.