If it is just plastic pieces, you can grind them away with a dremmel. If the back of the heater box (which is also plastic, but you can tell the difference) you will need to heat it and bend it back. Get the heat gun and a 2x4 that has been rounded at the end. Large amounts of heat can cause a windshield to crack, and even though you probably won't get it that hot, it's a good idea to take precautions. Tape some paint sticks (or something else about 1/8" thick that isn't meltable) to a piece of aluminum about 1 square foot. Tape the whole assembly to the windshield near the heat gun. This will keep the windshield cool. Anyway, put the heat to the plastic heater box, and with the 2x4, poke it easily until it becomes soft. Then remove the heat and slowly push the soft plastic back with the 2x4 and hold it there until it cools. To another test fit with the speaker and repeat as necessary. If you manage to poke through the heater box, don't panic. if the hole is small enough, plug it with hot glue or duct tape. If the hole is a little bigger, use a bigger piece of duct tape and spread hot glue over it.