Yippee!!!!!
I saw the light at last. Not only it *is* possible to add content to drupal from a command line script with existing tools but, apparently, somebody else already did it.
I am really, really, really embarassed to not have thought to this approach since day one (*) but you simply have to login and provide the values of the normal drupal form... with curl. Again, I have _not_ tried it myself yet, but once I remembered that this tool exists and what is its purpose, a google search immediately found these pages:
http://www.voidberg.org/blog/python_symbian_gps_drupal_and_google_maps.html http://ruk.ca/article/2603 http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/267255
which seem to confirm that it can (is being) done.
Hope this helps everybody else who wanted to know how I would deal with this problem. Note that, if ran on the server after uploading everything via scp, this _may_ also increase security, reducing the number of times you have to send your unencrypted password over the internet.
Ciao,
Marco F.
(*) my only consolation (said friendly, please don't be offended) is that in all the weeks I asked here and on the forums _nobody_ else thought of it first :-P