I can't see how this would work in a L2L setup, where no software or information is actually configured or pushed to the end client. In a L2L setup the end PC has no idea there is a L2L tunnel in between it and the remote network, so there's no way you could have it send particular DNS requests to a particular DNS server.
In a remote VPN setup, this is all handled by the installed VPN client, where it intercepts particular DNS requests before they go out in the clear and it encrypts them and sends them over the tunnel. This is not possible without the VPN client software installed.
