As for creepiness, you know what's creepy? People saying something and then lying about it later.
You'll be happy having the audio even if there are restrictions. Simply don't tell anyone about it until the benefits (saving your ass) outweigh the drawbacks (potential charges).
To circumvent the one-party consent issue, he could just write a Terms of Service on the inside of his shirt that includes a clause about "Engaging in conversation as a use of the Services" that implies agreement with the Terms of Service.
You'll be happy having the audio even if there are restrictions. Simply don't tell anyone about it until the benefits (saving your ass) outweigh the drawbacks (potential charges).