How to preseed.cfg with official installation cdrom

[Mario Gummies <qemu-buro-point-dpkg@yandex.com>]

Hi,
I am planning a fancy debian installation session next week on a real machine and I want to do it with the preseeding method called "file". Therefore I downloaded and burned a cd-image from the official server. Please note: This is not a case of a mastered cd, I speak of. Given I found a preseed.cfg, which I put in a parallel partition on the hd, ready to be loaded into the installation routine.
Reading the docs here is the point, where I loose track: 

This case, loading a preseed.cfg within an ordinary cd installation from hard disk, seems not included within the examples given, does not it?

These are btw the terms I did web search for:
installing preseed from file cdrom  debian-boot@lists.debian.org

Any idea or discussion on how to perform it, any pointer?
Tia