That hex screw holds in the metal cap part which holds the spring - I've pulled one of mine apart, after Don told me what the hex key size was (I think it was 3/32", but if you email Don he can probably tell you, I can't remember if thats it)
Beneath that metal cap there is a plastic piece which seems to attach to the rubber boot of the switch. I haven't been able to get that bit out yet..
You can actually just pull the spring out - it is only held in there by compression/friction.
Don has pulled these things completely apart - maybe he'll poke his head in and point us to some nice photos..
Graham