View:Allow, View node: Deny - Can I add a message to the blank homepage?

I've set my Unregistered/Unconfirmed users's General Permissions to:
View: Allow​
View node: Deny​
(And all other settings to Deny)​

This creates a blank homepage with a sign up button that looks like this:

Is there some setting or function (or a trick!) that would allow me to put some kind of introductory or instructional text in the huge blank space?