One entertaining possibility would be Pidonus witnessing Lelouch using his trick on Yuri... Then pointing it out. Possibly but not necessarily right in front of Yuri. She's smart enough that she'd recognize an implanted trigger, but being her, wouldn't think about how he did it until he tried it on her (probably with the exact same Geass - standard Deal With Suspicious People Language - or possibly something a little more amoral-psychopath).

I'll try to write a post tomorrow, perhaps? I must of course come up with what goes wrong... Pascal after all isn't the best of taking care of even herself.

EDIT: Also, I added Pascal to the permissions post because I rather like the idea of a more villainously-minded character 'convincing' her to help them, if Lelouch develops any suitable plots. Of course, being Pascal, it could go wrong hilariously. "Serve as my mad scientist!", for example...