I need to install an alarm inside a Honeywell TG512A 1009 Universal Thermostat Guard (plastic case). The alarm has a small speaker that is approx. 2" in diameter. I would like to cut a hole that is about 2" in diameter that would be coincide with the alarm speaker. What would be the best way to cut the hole? I need to do this to about 100 units. I have a drill press and can easily build a jig to hold the plastic guard in place. Thank you.