Hello John,
No, that wouldn't be possible. Any page in Joomla! would trigger the GeoBlock. This means that the redirection to the landing page would trigger the GeoBlock which would redirect to the landing page and so on and so forth until the browser would throw up the hands in the air and say "too many redirections". You can, however, include a link in the message (presumably a static HTML page in a subdomain) explaining why someone is blocked by GeoBlocking or any other reason.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!