This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
If you abandon the use of the session (no bad thing, by the way) and redesign your applicaitons to send state with the request that would work. Otherwise you will need some common persistence mechanism to share the data in. FTP doesn't sound the like the right mechanism, things will always be out of date. If you can't use RMI either this is harder to do - I was going to suggest a distributed cache, but distributed caches are RMI based.