\documentclass{article}

\usepackage[a4paper]{geometry}
\usepackage{graphicx}
\usepackage{pdfpages}

\pagestyle{empty}

\newcommand{\mainfile}{../main.pdf}

\begin{document}

\includepdf[nup=1x1, noautoscale, pages={last-last}, pagecommand={%
\begin{picture}(0,0)(-470,612.2)%
\includegraphics{bookspine_res.pdf}%
\end{picture}%
}]{\mainfile}
\newpage
\includepdf[nup=1x1, noautoscale, page={1}, offset=-14 0]{\mainfile}

\end{document}