Audio Cloning AudioMixers or Groups?

Is there a way to make instances of mixer groups at runtime?

Our use case is to make a series of sound loops that can each have their filters modified at runtime, independently. Some example code:

Code (CSharp):

1. var mixer = Instantiate(pfbMixer);
2. mixer.audioMixer.SetFloat("Pitch", Random.value * 2);
3. source.outputAudioMixerGroup = mixer;

This results in the cloned mixer having no influence on the audio source. Does anyone have any advice on how to approach this?

Copying the toplevel mixer also results in a "cloned" mixer that ends up being a proxy to the original mixer anyway, rendering the cloning pointless.