Installer annoyance - a bug?

[Richard Owlett <rowlett@cloud85.net>]

There is *functional/quality/?* difference between an install from a 
physical CD/DVD and from an "equivalent" flash drive.

I have a very atypical use case:
  1. internet is *not* available to support installation.
  2. my goal is what I consider a minimalist GUI

When I first used Squeeze:
  1. an internet install was impractical as I was on dial-up.
  2. physical CD/DVDs were readily available
  3. after booting into a minimal command line system my custom
     system could easily be installed using apt-get

Although I now have high speed connectivity, my data cap is low enough 
to strongly discourage ANY installation related internet usage.

I can easily install a command line system. BUT installing desired GUI 
components via apt-get is impossible because it searches for a 
*non-existent* physical CD/DVD.

An install using a preseed file is possible but I find it cumbersome.

Is there some way, during the initial installation, to drop to a 
terminal to specify additional packages to be installed. As preseeding 
can do essentially the same thing the required framework must exist.

TIA