Adding Chat to Ultimate Member profiles


I am building a website using the Ultimate Member plugin for profiles. I have their Extensions bundle, which includes Activity wall, Private Messaging, Following, etc. The only thing missing is an Instant Chat ability.

I know WPMUDEV's CHAT plugin can show people online via the admin bar, but that will be disabled on my site (front-end only). I'm not using BuddyPress or Friends either, so there's no way to connect with people online via those methods.

I just want a way for people to see other users online and be able to instant chat with them, but through Ultimate Member. UM has an "Online Users" extension, and there's a way to code extra "tabs" on member profiles that can display custom content.

So how can I provide a way (a button or whatever) for people to start a new instant chat with someone? Any help, suggestions or guidance would be greatly appreciated.