Custom Closed Captions Button

We are using a custom player with on-screen previous/next buttons, menu etc. but want to enable closed captions in some screen recordings.

Is there any way to turn captions on/off using a button on the slide itself? I guess what I need is a special trigger that does that but it doesn't seem to exist!

Any workarounds so I don't have to have the horrible button bottom left off the slide!