Instead of having an actual track in the song controlling the ducking, create a separate ReDrum whose audio output is connected to the sidechain input of the compressor. Then create your special "beat" that will control how the sidechain pumps.
And to take this to the next level, use ReDrums velocity options to change the volume of each beat, which will take your sidechain sound and turn it into something groovy that works in almost every genre.
Here's a detailed video of how to do it: