Call a sentence trigger only if the sentence doesn't match a preconfigured sentence in assist

I am starting to setup my own Voice Assistant system using HA. Since I build some pretty complex automation, sometimes I move my automation logic outside of HA and into another system (AppDaemon). Something I would like to do is to have an automation to handle voice assistant sentences that do not match any of the built in sentences and forward those (using a trigger which fires an event) to AppDaemon.