From the ADSL (site A) you must configure 4 VPNs in client mode and remote server the IP address of a ZeroShell Box that you have in the place you have the 100Mbit/s Internet connection (site B).
In the site B you have to create 4 VPNs in server mode. Do not forget to change the UDP/TCP port number (the same for the site A).
Now you must put all the VPN interfaces in a BOND interface from the site A and from the site B.
At this point your BOND interfaces are connected and look like ethernet interfaces: you can assign them IP addresses if you want to use the routing between site A and site B, or bridge them with physical ethernet interfaces if you want to connect site A and site B in layer 2. In latter case you can transport the VLANs too.