Restricting the chat entry form to certain roles

I have three user roles on my site:

- Anonymous (not logged in)
- Standard (Registered users)
- Premium (Paid users)

Right now, I only use the chat plugin in a single location embedded on a page via a shortcode. I have the chat plugin setup so that anonymous users can see the chat, but not post to it. I would also like the "Standard" users to be able to see the chat, but not post to it. Leaving only the "Premium" users to actually be able to chat. Everyone else would just be a spectator. However, the chat plugin doesn't seem to allow me to do that. It looks like it always allows logged in users to post, which for me includes the Standard and Premium users. Is there a way to control that? Or possibly a short-code modifier that could remove the text entry area? I use a membership plugin that could easily allow me to substitute shortcodes based on user roles if that is the case.

As a last ditch effort, I could do some CSS trickery to remove the field, but I would prefer something supported by the plugin.