On my network I'm thinking about always tunneling a specific client. Is that doable?

I have an appletv on the network with an internal ip and am thinking of getting an us vpn service.

The question is if I set up a l2tp client on my routerboard 450g, can I have it forward just that IP over vpn tunnel or do I have to set a specific port (fortward lo3 -> l2tp client)

How do I do this? What is the best way?