Saving sessions during server failure

We have an applilcation running on .net and our dev group is working on trying to write session persistance. I KNOW the F5 can do this, but need to get them started. I am not a developer but have worked with some basic irules, etc. Currently, when users are logged on to a server and that server goes down or is removed from the pool due to a health monitor, they lose their session. They have to close their browsers, then log in again and start over. Currently our application runs using the In-Proc configuration where sessions are kept as live objects in web server (aspnet_wp.exe) thus, when the webserver crashes all the sessions are also gone and users can’t continue with what they're doing. Ideally, we want to be able to cache their sessions so when they are bounced to another server in the pool, they can resume where they left off. What is the best way to do that? The standard cookie or source persistance profiles don't save their work in the application. Can F5 do this or does it need to be written into the application? Action on "Service down" is set to "Reselect."Any suggestions are appreciated. Thanks, Chris