That option does exist, but only on master; it was not in the 0.66
release. It turned up by mistake when I updated the documentation copy
of the Plink online help while preparing the 0.66 release, because I
ran plink from the wrong branch.
The new release automation should stop that kind of mistake from
happening in future.
\c -N don't start a shell/command (SSH-2 only)
\c -nc host:port
\c open tunnel in place of session (SSH-2 only)
-\c -shareexists
-\c test whether a connection-sharing upstream exists
Once this works, you are ready to use Plink.