$3 piston stop
Go down to the auto parts store and ask them of they have anything called a 'spark-plug non-fouler'. They'll say nope. Then tell them you need something that screws into the head to keep the sparkplug out of the combustion chamber and thus, prevents it from fouling. They'll lead you right to them.
Usually they are sold in a 2-pack. Get the ones that match up with your plugs (tapered seat or oil-control ring). They will be about $2 for 2.
Go home, select a drill bit that will go through the middle of it and take care of the restriction on the end where the plug tip sits. Then tap the sucker.
All-thread is my choice for the center portion. It isn't nearly as strong as some bolts...you don't need something super strong anyways. Slot one end of it. Thread it in (you tapped the non-fouler with the same threads as your bolt or all-thread, didn't you?).
That pretty much sums it up. It is a heckuva lot easier than drilling out a spark plug. Or uh, so I hear....




