You can designate the Word Startup Folder but not the Office one, AFAIK. There is no provision for a third. This link has everything I know about the Startup Folder and has links to other resources.

IMO the startup folder (and contained Global Templates) and Workgroup Templates Folder should be local, not network. There can be a central repository for these files on the network which is updated upon user login. Doing this makes use of laptops more feasible, cuts down on network traffic, and makes updating the shared resources easier.