punchvpn routers do exactly this. They divide the network into to sub network. ISP and VPN. You can then assign the physical network switch to go via ISP or the VPN route. Any device connected to the network switch with VPN route, will use VPN only. For the wifi network, there are two ssids...
if you wanna purchase a router which can automatically do Samba over VPN (PPTP or L2TP/IPSecure), then try googling punchvpn router. This router is based on Openwrt. It even has web based file upload/download via VPN for IPhone/Android in addition to samba.
try punchvpn Openwrt based routers fropm punchvpn.com. Its a VPN router which enables VPN sharing not only from your home/office but also when you are away from home. They have Remote access feature which will enable access to router's VPN connection when you are away using your smart phone...