I don’t know if its already a feature, I can’t find it.
I use torrent indexers only, and since KAT died and RARBG stops working from time to time, I had to add a custom RSS feed, which works perfectly, the only problem is that the video is cut into several rar files. Sonarr obviously can’t unpack the video file, I do that happily. Only problem is that Sonarr still keeps looking for the episode so I always have to manually toggle the monitored status for these episodes.
I think there should be an option to stop monitoring an episode after it was downloaded. Now it only stops monitoring after it was copied/hardlinked.