I see that the author had planned to add this feature since the inception of this plugin but apparently never had the time and/or need to get about it - https://discuss.flexget.com/t/plugin-dev-magnet-to-torrent-file-convert-magnet/553.

The reason for this feature request - recently one of my tasks accepted several poisoned torrents containing invalid .zip and .wmv files with, no doubt, malwares in them. I have a content_filter in place that would reject such entries, but in these cases the convert_magnet timed out and let the entries through. I have since increased the timeout value but I doubt it's a network related issue.