Custom partitioning shell script?

[Matthew Palmer <mpalmer@debian.org>]

I have really simple needs here -- I just want to (effectively) replace the
entire partitioning phase of installation with a single shell script -- I
need to do all sorts of interesting things with partitioning, but I can
easily write it out.

Is there a quick-n-easy way (or already-documented method that Google isn't
telling me about) to do this?  I'm just hoping that somebody's already done
this, and can either tell me how it's done, give me some hints, or tell me
that it can't be done.  <grin>

Any help *very* greatly appreciated.

- Matt