Enable similar topics popup for private message composer

I’m trying to make it easy for users to send private messages to a support group alongside the public community topics. I would like the “Your topic is similar to…” popup to show while they are writing a private message to the support group just like it would if they were creating a new topic to help them notice any public topics that already address their question.

I couldn’t find any setting or plugin that can enable this, does this seem tough to implement as a plugin if there’s no existing way to do it?