I really like the look of those fizik saddles with the bright little tail light just underneath the back of the saddle...surely someone has found a light that either takes advantage of the "classic" bag hooks on the Brooks saddles, or otherwise puts that gap between the leather and the seat bag to use by fitting a snazzy light in there.
I've been looking for this, too. I tried a DIY solution with a couple of hose clamps, but it wasn't great. I'm very pleased to see cateye has a new saddle rail mount coming out. I hope it works on Brooks'.