looking for apt.conf reference

[GCS <gcs@lsc.hu>]

Hi.

 I am trying to fabricate a script, which runs as a _normal user_,
checks my debs in a specified directory, and recursively download all of
the dependencies. I can iterate on the packages and get the dependencies
parsed from 'dpkg-deb -f package', but how can I download packages? I
have thinking on something like:
apt-get --download-only -o Dir::Cache::Archives=store install zsh
But still, apt-get would like to place the lock in /var/lib/dpkg/, where
I do not have write access. How can I change this? 'man 5 apt.conf' does
not help what config option should I override, and I was unable to find
a complete apt.conf reference. The best I have found is:
http://www.debian.org/doc/manuals/apt-howto
But does not contains an apt.conf reference.

Thanks for any pointers in advance,
GCS