Unfortunately, this isn't something you're going to be able to find out from within the Soundflower kext because applications don't connect directly to audio drivers. The Audio HAL is an audio driver's user client and manages audio input and output between apps and the kernel.
You should look into using a HAL Plug-in. Your plug-in code will get loaded by any application that uses Core Audio and you can do whatever you need to do from there and use some IPC to communicate with your driver and app.