Hi TeachMeIT and everyone,
If I understood your “problem”, what you are asking is in some way similar to this question, which I answered.
Basically, the first thing to do is create the wan link to the “main” office. Once you gave a connection in each branch office, you just need to configure or ask your provider to do it for you, a local subnet different from any existent. After this, you need to configure a DHCP Relay Agent in each subnet in order to be able to forward all DHCP requests to the main office/DHCP Server.
I think this is a straight forward process. If you need further clarification, please let me know.