Routers / Switches :: Network Subnet Range To Wide For Vpn?

I have a supplier which i need to connect a site to site ipsec vpn connection to (from a draytek router). I have already done this on our main site with no problems using the local ip details of 192.168.1.0 and subnet 255.255.255.0 however i need to do the same on our DR site which uses the ip details of 10.1.0.0 and subnet of 255.255.0.0. Our supplier told me the 255.255.0.0 is already used at there end by a different customer so we are unable to connect the vpn and communicate (in theroy we can connect but our supplier cannot reply). We can setup a connection to another spare server on a different address using a different subnet but effectivly this would mean that communication would stop at that server and communcation to the overall network or specific server the supplier needs access to (on the 10.1.0.0 255.255.0.0 network) is not possible. I was thinking maybe an internal vpn server to server connection through win server may do it, 2 nic cards or routes in the server routing table but this all seems a bit messy. Our network consits of win 2003 and 2008 R2 servers and is basic network with modem-vpnfirewall-switch and devices on the internal network connecting to the switch.