Thanks again David. I really do appreciate your input. But unfortunately there are still some issues here - it's still not a straightforward solution, and creates other problems - for those keys with longer labels they would overflow the box, so ideally some 'scale to width' capability would be really helpful. I don't see that with this type of utility.
You are right that the platforms do impose some restrictions around what can and can't be done, but there are several examples of how you can use different font sizes (such as in web pages, or in emails, or in the various office-style apps that are available). It feels like it ought to be possible to be more flexible.