Pitlock sells a small steel cable lanyard that you loop around the rails of your saddle then use the other loop to connect to the pitlock seatpost clamp. Look at this pic, it's there but kinda hard to see. It's just like those full size cables you see at shops. Some shops even carry those small lanyard cables...

I myself use an old single speed bike chain. Just like Treebound... use a chaintool to trim a length of chain, then use a old road tube cut to same length. Drop the chain into the tube then wrap tube covered chain around the rails of your saddle and top tube. use chaintool to reconnect chain.
Anyone whos gonna want your saddle not ony needs tools to remove it, but they're gonna have to earn it as well. I also will use a waterproof saddle cover or a shower cap to help "camo" my Brooks Flyer in high theft hotspots. these methods help and, may give a little piece of mind.