How do you remove a broken stuck spark plug boot on a subaru outback?

It helps to have a small light to look down the tube to see what's going on. Then, spray it with silicone spray. Then push/pull a long 1/8" or 3/16" screwdriver all around between the spark plug ceramic and the broken piece. Then do the same between the piece and the tube wall. Then work the screwdriver at an angle, trying to rotate the broken piece under pressure, as you slowly pull the screwdriver out. Repeat. Check with the light. When it's worked out a little, or if you get bored, take a long handle long nose pliers, open it as much as possible on the edge of the rubber piece, push in and grip...then pull. Repeat and check with light until you get it out. I had 3 out of 4 boots break on a 2002 Legacy, and this is how I got them out.