Can I configure openvpn connection between two offices that will use the balancing

Can I configure openvpn connection between two offices that will use the balancing between two ISPs

there is a router with Vyatta which included two usb modem

they tuned to load balance of traffic

if I install openvpn connection, this connection will use only one of the channels
Also I can configure two openvpn connection and customize their load balance, but how to bind openvpn connection to a particular Internet link