WOL with a remote control software such as TeamViewer or LogMeIn), is connected to the internet and has uTorrent and the Dropbox client installed. Of course you also should have the latter installed on your mobile device too from which you want to initiate the torrent download.
After you've installed all the required software, start uTorrent and under 'Options' go to 'Preferences'. Under 'Directories' put a check mark at 'Automatically load torrents from..' and create a new directory in your Dropbox folder with a identifiable name such as 'torrents'. As a result, all torrent files that are saved in that directory will be automatically launched for downloading provided that uTorrent is running in the background (normally in the tray bar).
Let's say you are still on the road or at another place than your home but want to download a torrent to your home PC from afar. All you have to do on your iPhone is go to your favorite torrent website, tap on the file you want to download, tap 'Open in..', select 'Dropbox' and save it to the 'torrent' folder you've created previously. The uTorrent client will automatically notice the new file in it's watch folder and will start the download of the torrent on it's own.