We can offer you a customization to take care of this.
The new behavior would be a landing page that only renders if you go to the community base URL. If they try to navigate to any other page on the site, they will be redirected to login.
We can accomplish this for a flat $1,000 customization fee with a guaranteed 45-day turnaround time from time of signature. We'd waive the $50/mo. customization maintenance fee.
We'd expose a WYSIWYG editor for you in your control panel to control the contents of this landing page, as well as an option to enable it (it would be disabled by default).
If this is something you'd like to proceed with, just let me know and I'll prepare something for you to sign!