[Jamesp]

In this situation I have drilled through the bolt then used progessively bigger bits to remove bolt material until the drill reaches the thread inner diameter. Expect to use five of six bits each just slightly larger than the next. Use an adjacent hole and a drill depth stop so you don't drill the head. Pay close attention to lining the drill up with the axis of the bolt. When the inner thread diamemeter of the bolt is reached the bolt usually loses structural integrity and can be removed with an easy out or occasionally a screw driver. Whatever you do don't break the easy out in the bolt. Good luck. If you are really lucky the bolt breaks loose while you are drilling it.