Any way to force umounts on busy mount points?

[B. Ferguson]

Does anyone know how to force a unmount of a file system, from a busy
mount point?

We service a number of workstations from a central file server.

When we re-boot the server, we get flooded by Stale NFS file handles.
Is there any easy way to umount these file systems without having to
re-boot the workstations?

Help would be apprecited,

Bruce.