Share Session Vars on 2 servers

I have developed a well tested password protection system using session vars. We have 2 web servers with half of our pages on each (for reasons I wont go into). What I need to be able to do is have a single login that would then work on both servers. Which basically means sharing session vars on 2 servers. Yes sure I could use just straight cookies because both servers live under the same main domain but I have the system already in place and I dont want to change it. I think it could be done by forcing the 2 servers to use the session temp same directory with 'session.save_path' variable by using a NFS share. But we would prefer not to do that. And in fact if that was the only solution we would just do without. Is there soemthing else I can do. Paul