Alright, this DOES WORK, but the explanation falls a bit short.
To get this to work, one must copy the whole bootcamp dir from the Leopard DVD to the hard drive. Then open the Bootcamp.msi in an msi editor, like Orca (
http://www.technipages.com/download-orca-msi-editor.html), or something similar, and remove the LaunchCondition table (right click -> drop table), then save and close Orca.
This means that the msi will not check anything when installing things... not even if you have administrator access to install the drivers. And without admin access it won't install directly. The easiest way around this is to launch the setup.exe, which goes into admin mode and launches the msi file.
Doing this, the install process seems to go without problems
Thanks rebk0r for the tips to get this working 🙂