I'd really like to have a nice saddle on my urban bike, but I don't want it to get stolen, and I don't want to have to lock it up every time I go inside, and I don't want the ugly lightweight chain locked to the top tube that I'm using now.

Has anybody tried using a 3mm cable "seat leash" around the saddle rails, through the seatpost and seat tube, and looped around the bottom bracket? I've seen these 3mm cables on Amazon, and it seems people usually use them the same way you use a regular cable (with a lock); but is there any reason I couldn't run it inside the frame? (Is this a bad idea?)