Producing crop marks fit for octavo signature layout

Question

Normally I use the crop package within a book class to produce individual sheets with crop marks. Now I would like to produce sheets for octavo signature binding, that is, eight pages on each side of the large sheet where the inside margins between even and odd pages do not crop because they fold. I know how to put the "mosaic" together from the PDF produced by pdflatex, but before I do that I need to add the crop marks and position the text area on the pages properly. I seem unable to achieve that with the crop package.

I can remove the inside crop marks with:

\usepackage[cam,a4,center,mount2]{crop}

But I seem unable to shift the page area to make it flush with the inner border. What I want to get is this:

Of curse I know that the centered option should not be part of the final solution, but if I remove it the text area flushes to top left on all pages, so I left it in here for the purpose of illustration.

Also, I know I could technically have the crop marks only on every 16th page, and that would be fine if it were the case.

I am looking primarily for a TeX solution (configuring or replacing the crop package) but a command-line tool to assemble the signatures and add crop marks would be a perfectly acceptable alternative.

Answer 1

Actually, combining includepdf and crop seems to work:

\documentclass{book}
\usepackage[cam,width=25cm,height=35cm,center]{crop}
\usepackage[utf8]{inputenc}
\usepackage{pdfpages}

\begin{document}

\includepdf[pages=-,noautoscale,landscape,signature=8]{mydocument.pdf} % Document is A5 format

\end{document}

Answer 2

A partial solution if you could switch to memoir class:

\documentclass[showtrims]{memoir}
\quarkmarks
\setstocksize{20cm}{16cm}
\setpagemr{16cm}{12cm}{*}
\setlrmarginsandblock{30mm}{15mm}{*}
\setulmarginsandblock{40mm}{20mm}{*}
\setheadfoot{5mm}{5mm}
\checkandfixthelayout

\makeatletter

\let\mytmarktl\tmarktl
\renewcommand{\tmarktl}{\ifodd\c@page\mytmarktl\else\relax\fi} 

\let\mytmarkbl\tmarkbl
\renewcommand{\tmarkbl}{\ifodd\c@page\mytmarkbl\else\relax\fi}

\let\mytmarktr\tmarktr 
\renewcommand{\tmarktr}{\ifodd\c@page\else\mytmarktr\fi}

\let\mytmarkbr\tmarkbr 
\renewcommand{\tmarkbr}{\ifodd\c@page\else\mytmarkbr\fi}

\makeatother

\usepackage{lipsum}

\begin{document}

\lipsum\lipsum\lipsum

\end{document}