simply go to the library and click the export button.
There you select as export-format: "Magma (YAML)".
This exports every file you share into a magma-list which other phex users can use to downloads your files automatically.
To increase the chance, that your buddies get the file, you can check the box "add my IP to the magnet-links", but when you do this, the magma-list will contain your IP and so it will compromise the little anonymity you have in Gnutella.
You can get more information at
http://gnufu.net/MagmaGuide