It would be very useful if you could add webseeds to your p2p program.
In my opinion there are two ways to realize this system. Someone adds the server as ftp and it appears as new client in the network, but he is able to control it,
Or, second option: You add a personal ftpserver to your own filesystem, so it appears under the section of your added files.
The second option would mean a greater control, because your computer has to run if people want to access the files.
But the first option would guarantee a steady availibility of files.
In both cases you have to hide the real ip and url of the server if possible.