Pitlock offers
saddle cables; it's hard to tell, but if you
go here and roll the mouse over the saddle and seattube clamp areas, you can see in the pictures the cable being looped around a saddle rail, and the end-loops going around the pitlock seatpost-clamp bolt, which would secure your saddle (assuming you can trust the strength of the cable). Worst somebody could do is loosen your saddle bolt, maybe leave it dangling (or leave it loose so it falls off when you sit on it).
I have seen other people "securing" brooks saddles with light steel cables like that, but it's a question of what do you attach the cable to?
BTW torx screw I don't see as very secure. If a good thief doesn't have a torx on him, if he spies your bike in the same place more than one day in a row, he can count on coming back with a torx later.
And of course there's always an angle grinder. There are horror stories out there of bike thieves at work for a surprisingly long time with tons of passersby doing nothing.
Pitlock seems as good of a bike security solution as I've ever seen (but I've never bought them -- I'm fortunate that I only ever have to lock up in fairly safe suburban areas, and I get to roll my bike right into my cube every day, so I only ever bother with a cheap cable lock)