My mate Andy mounted his polar speed sensor on the upper leg of his Lefty Max and then put 3 magnets at about 1" spacing on the same spoke. The polar sensor is fairly forgiving, and there is a little flashy light that shows you when it has sensed the magnet. I have seen the speed/distance traces from his rides and the signal is very reliable - i.e. no loss of signal.
Cateye computers fit straight on (Mity 8 and the Enduro 8), no need to use the SEB adaptor. I can send picture if need be. The only "modification" is that you need to use the old style magnet that came with the cateye i.e. not the metal stud type. Failing that you can stick a small magnet to the arm of the disc rotor.
Or just use a cateye Astrale which feeds off the rear wheel and has cadence as well. Means that if you were ever to want to use a turbo trainer with it then you have speed / distance.
Thanks very much for the advice. I've got an earlier version of the Enduro which has always been 100% reliable, so I'll stick to that (hopefully without the need for a SEB).
I have just cable tied mine to the bottom of the fork leg just far enough up for the magnet to clear the disc caliper and cable. The forks don't seem to need to compress that far to foul the sender- at least not to date anyway. The sbs thing looks great but a bit expensive.
My LBS araldited the magnet on the Cateye Enduro to the disk rotor - seemed to fall off after a few months, so I gently filed the edges of the magnet down so it sits in the cut out of the rotor and can't get knocked accidently (also used superglue). Its been there for over 6 months now. Feed the wire back up with the disk hose and use a braided cable tidy over both - it looks pretty tidy.
I have a Lefty, tried wired and wireless nothing worked well. With wireless if you hit anything then tha magnet or sensor moved out of range, wired jsut snagged and seemed to be hassle.
I've ended up with a GPS which doubles as a ver accurate but pricy speedo!