it cost around 1gbp for the screws and about 20-30min of work.
the seat is now 3-4cm lower when you sit on it, hold the legs better, and it doesnt feel much harder
sorry for the low quality - shot with camera phone
http://avance70.tripod.com/seats1.jpghttp://avance70.tripod.com/seats1.jpg
http://avance70.tripod.com/seats2.jpghttp://avance70.tripod.com/seats2.jpg
http://avance70.tripod.com/seats3.jpghttp://avance70.tripod.com/seats3.jpg