Add Label Text to existing Toolbar Button

Hello,
Hopefully what I am looking for should be quite straight forward but I have searched the Developer Guide, API Reference and Forum but not found it yet.

I have a "reduced" toolbar toolset but would like to make the "Templates" button include a textual label to the right of the icon - just like the "Source" button has.

Can anyone advise on how I do this?
My page contains a single instance of the CKEditor and associated toolbar.

Thanks.