jbweld something that will fit snuggly than try it removing that

 

I did this on a motorcycle I had once. I took a very large flat head screw driver, tapped it firmly into the hole with a hammer, and turned the threaded portion of the spark plug left behind, out. Worked like a charm.

 

Yep, it's kind of like a bearing puller.

Tack welding could also work...

Just dump a load of oil into the engine through the plug hole afterwards and slowly rotate the engine while blowing through with compressed air and the debris should go out through the exhaust.