I'm just starting w/ Django, so I may be a bit off, but the way I'd have liked to see the setting of DJANGO_SETTINGS done is like what Perforce does with its configuration files. Specifically, a combination of environment variables (with a Registry-persisted version on Windows, although that's less relevant for Django probably), and configuration files which you can sprinkle in your filesystem to define "context". So that if you had two different django projects you wanted to switch between, you just need to create two special files in the root of each project, and set _one_ environment variable that django-admin would then use the appropriate configuration for that project. Maybe not well described -- see the p4 docs for hopefully useful info:
http://www.perforce.com/perforce/doc.051/manuals/cmdref/env.P4CONFIG.html (hmm, that's not much better =). Let me know if I'm clear as mud (or if I'm missing something already existing, which is very possible!). --david