TVAD's hair dryer and vacuum suggestion is right on and has worked for me. You don't want to let the vacuum attatchment touch the cone. I would sugget you use the brush attatchment so there is some control over the amount of suction.
Dimple in speaker driver cone
I have a pair of Thiel CS 1.6s that have a quarter size dimple in one the driver cones of one speaker that a friends curious child created when he pushed his finger into my speaker (damn him). Can that dimple be removed by moi? Or do I need to have it repaired or replaced by the manufacturer?