Managing 40 different sites / 3500 users

So In our company, we have about 40 geographically separate locations, with a total of about 3500 users and about as many computers. Setting up a distribution server for each of those locations would be quite tiresome and not possible on many of those locations. Even having to specify the computernames in a text file before deploying the agent (to get them to use a distribution server instead of the primary desktop central server) would take enourmous amounts of time

We plan to use the primary desktop central server mainly to push out software installations and OS patches. How do you suggest we proceed? Most locations have a 10 mbit or 100mbit connection to our datacenter where the desktop central server is placed. So far I've only pushed out the agent to about 60 computers on the same LAN, which seem to work fine.