Maintaining ASP.NET Sessions

Question

Is there a way to mainain user sessions when replacing the project dll on the webserver? For example, I have 10 users logged in with active sessions. I have some changes to push to the server, so I have to replace the project.dll file in the bin folder. When I do this, its forcing the project to "restart" itself and all users lose their session. I have also tried making this a non-compiled web project -- where the aspx.cs files are referenced via "src" rather than "codebehind" -- so there is no dll, just individual files. This seems to help, but isn't 100% reliable and sometimes sessions are still lost. Is there any way around this? Thanks, -Chris B.