Force dismount NFS partitions?

[Dan Watts]

Does anyone know of a way to force dismount of an NFS mounted partition?
I've got some partitions mounted from a remote Sun which is now down.
Unfortunately, now I can't do a 'df'.  It just hangs waiting for the
missing NFS mounts.  If I run 'umount', it hangs too.  It eventually
comes back with an error that the umount timed out, but does't remove
the mount entries.

I'm looking for anything that'll work, even pointers to how I could
write a program to manually muck with system files if that would get
the #?$%@! partitions dismounted.
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