[xwiki-users] Set a Maintenance Start Page

Hi All, Sorry, this might be a silly question, but let's go: How can I set a temporary start page on XE, or redirect all requests to a specific page in running time? My need: during the migration from 2.4.3 to 3.0 I'm planning to do in the next few days, I would like that all users (except the admin) that try to access the wiki (the login page or whichever other one) be faced with a "The system is being updated and will be available at <ETA> bla bla bla". Our production server doesn't use apache, but direct on JBoss. Until users view the maintenance page, I'm working behind the scenes performing the imports and skin preparation etc. Thanks in advance for your help. Regards, Ramon Gomes Brandão