Hello Sloe,
Wondered much the same myself for use on my Catalyst. Could do with lowering the seat for sections of steep singletrack and giving my wife a bakky. Not sure that a proprietry seat clamp would work given the shallow slit on the seat tube, the clamp may be so wide that it binds on the complete tube without reducing the tube diameter. I've been chucking round the idea of fettling some sort of shortened bolt with a camming device to fit through the M6 bolt hole...possibly using a spare wheel skewer... the pressure faces of the skewer and acorn nut may be a bit too large to be effective though.
Having the allen bolt does deter some behooded n'eredowell from half inching your seat. Mind you a locked shed didn't stop them from lifting my wife's bike from the garden shed last week to fund whichever habit they've elected to succumb to, hence the need to go tandem...
