One way to make this work, is when you open the torrent file, you get this window pop-up showing all the files waiting to be downloaded. So what you do is uncheck the ones you dont want to download now (ie, all except one) and check the one you want to download. When that file is done, you right click on the torrent name and then properties. You will now get the same window poping up as before, but now you uncheck the downloaded file and check the next file you want to download, and so on and so forth.
The only problem with this is that you have to be at your computer when the file is completed to change to the next one. I am assume you are download a series of some kind.. lol.. I have done this many times, since download the first, watch it, and then the second.. etc.