First the legal part...
What you want to do is a violation of Tivo terms of use. Units on the same account are supposed to be at the same physical location.
Now the technical part...
There are a couple of ways to do this, one is fairly complex. What you would need to do is create a VPN (virtual private network) connection between the two locations. This requires a router on each end with VPN capability and reasonable speed broadband connections as everything going between the two locations would be encrypted.
Since you're talking multi-room viewing I'm assuming you already have a Series 2. Another way to do it would be to use TTG and transfer the shows you want onto a laptop. Then you could take the laptop to the cabin, connect it to the other Tivo, and use Tivo Desktop Plus to make the shows available to the other Tivo. The MAK would need to be the same on both Tivos and the laptop in order for this to work.
Hope this helps,
Ken