How to set up a particular VPN configuration...

I own several businesses that are all linked by VPN to the home office occupying address subnets 192.168.N.1 … where N=1 is the home office address space, and the rest of the satellite locations are N=2, 3,... etc. So far this works well to use all of the resources from one office subnet to another. However, I recently ran into a situation that I need help with. My bank checks that traffic comes from the USA proper... and two of my business locations are in the Caribbean. What I want to do is have computers on those subnets … lets say N=8 as an example, be able to route traffic from the satellite office 192.168.8.x to the home office 192.168.1.y, over VPN, and then out of that locations WAN connection such that the traffic appears to originate from my home office (and thus the banking connection works). I'm ok at setting up peer-to-peer VPN connections and provisioning VPN connections but this one is a little over my head. Any help would be appreciated.