I suppose the output to the pipe is so the StdinReader does not display
"Updating...", right?  Would it actually be possible to tell xmobar to run the
StdinReader but exclude it from its top-level output template?  In that case, it
doesn't matter what is sent to the StdinReader - it would never be displayed.
What I'm not sure about is whether xmobar would actually run the StdinReader and
see the EOF.  (I don't think xmobar checks whether a monitor is in the output
template before starting the monitor.)