How can I make the client think they're whispering someone

My game has a shadow mute feature derived from this. The user thinks they’re sending messages but the messages that appear on their screen don’t appear for any other user. It’s really useful for moderating rude or nonsensical users without them knowing.

However trying to whisper other users doesn’t have the appearance of working for them and is a pretty clear giveaway. When a shadowmuted user attempts to whisper someone else, it looks like this instead of looking like they’ve actually whispered them.

I would like to try to get around this by making the whisper appear successful/normal to the shadow muted user. But the only method I know how of doing this is creating chatspeakers, which seems a little excessive for a tiny task. Is there a simpler way to modify the users’ message or speaker data so that it looks like their whispers work like normal?