\documentclass{article}
\let\oldthebibliography=\thebibliography
\let\oldendthebibliography=\endthebibliography
\renewenvironment{thebibliography}[1]{%
    \oldthebibliography{#1}%
    \setcounter{enumiv}{77}%
}{\oldendthebibliography}

\begin{document}
This is a test.  Some newer thing
about a canonical quantum gravity approach\cite{rovelli2004}.
\bibliographystyle{plain}
\bibliography{biblio-physics}
\end{document}
