TomatoUSB

How can I use my asus rt-n16 with tomato to supply wifi+vpn to existing router? I have a peplink balance 20 that I recently purchased and I have the tomato behind it with dhcp off and set to "router" mode instead of gateway but I am uncertain how or if its even possible to use tomatos openvpn to connect to the network and access all files and such on machines connected to the peplink balance 20.

Any advice? Thanks.