Nobody's strung all that together for you, as far as I know. If you're handy with a compiler, you could perhaps build something yourself, though.
Here are the pieces you need:
- A Firefox add-in. (You want to click a link on a client and have something happen on a different machine.) Possibly you could instead create a program which would serve as the default for opening torrent files, and would forward the request to your server.
- Some sort of communication channel between your client and your server (this isn't supplied by Windows Home Server), probably supplied by a service on Windows Home Server to queue up your torrent request.
- A Windows Home Server add-in to monitor the status of torrents (which ones are still downloading, seeding, etc.)
I'm not on the WHS team, I just post a lot. :)