Creating a multi-book manifest is not currently documented. However, it's not too difficult to do. I know a few companies who have successfully done this.
On the VS 2010 product DVD is a folder called \ProductDocumentation.
This is where you will find all script and packages used to install VS help from local disk.
To load all documentation from DVD:
So to emulate the multi-book setup this file is where you start
This file points to 2 other files, product1.html and product2.html. And these product files link to all 14 or so books and their packages.
There are various settings that MS use for downloading of packages. These can be ignored for offline install. You probably need to defined unique package-etag IDs to make the install work.