Interestingly, after a mere 136MB (of the FinalBuild folder's 460MB), the game launches to the menu without a complaint. If you explore the frontend - fire up the game encyclopaedia - then you can see that there are some textures missing, but running Mc2Rel.exe in the FinalBuild folder also appears to be missing these textures.
So, I've got a "working" minimal deployment. I suspect that if I actually tried launching a level it would complain some more, but I don't necessarily need to be launching levels yet. I know I'd like to work on the renderer, but there are other things that could be interesting to fix - specifically, MC2 currently wins no Best Practices awards for saving all of its data (including user prefs and savegames) in the Program Files/MC2 folder, which is no good if you don't have write permissions to that directory. I should be able to modify it to use the user directories correctly, maybe even implement launchable savegames.