RequirePackage{filecontents}
begin{filecontents}{mybib.bib}
@preamble { " providecommandnoopsort[1]{} " }
@misc{x1,
  author = "noopsort{ZZZZ}Anonymous",
  title  = "Random thoughts",
  year   = 3001,
}
@misc{x2,
  author = "Author, Annie E. ",
  title  = "Deep thoughts",
  year   = 3002,
}
@misc{x3,
  author = "noopsort{ZZZZ}Anonymous",
  title  = "Further thoughts",
  year   = 3003,
}
@misc{x4,
  author = "noopsort{ZZZZ}Anonymous",
  title  = "Final thoughts",
  year   = 3003,
}
end{filecontents}

documentclass{article}
bibliographystyle{plain}

begin{document}
cite{x1}, cite{x2}, cite{x4}, cite{x3}
bibliography{mybib}
end{document}