[Jager]

You might consider using something like this to get inside the cover and try to remove the pieces:

http://www.amazon.com/Bosch-PS90-1A-12-Volt-Optical-Scope/dp/B0046ZRYOU

http://www.amazon.com/MAXCRAFT-60184-Lighted-Magnetic-Pick-Up/dp/B0042D6H44/ref=sr_1_5?s=hi&ie=UTF8&qid=1342974684&sr=1-5&keywords=flex+tools

You might have to pull-out the other spark plug tubes to see and get to the broken pieces.