Tools -> Options -> Files -> When opening a torrent, show options dialog...
Make sure that is set to "every time".
Add the torrents you need to do this with, select all files in the window, and unmark. They will go straight to the seeding list, but there's one more step: change their "fake report to tracker systems" or ratio tool settings to show yourself as a seeder. This will make the tracker see exactly that, and since you told Vuze you aren't interested on any files when you added the torrents, none of them will be downloaded or written.