does pressing on the internal button work correctly??
if so then you could glue or epoxy something to extend the button for easy access, but if the problem is not resolved by removing the rubber button cover then your problem is an internal electrical issue (maybe due to liquid leaking into the battery) and if that is the case there is not much you can do to fix it.
as long as the 510 is so popular, most manufacturers are not going to concentrate on fixing a flaw in a product which they don't sell alot of.
your best bet if you want to continue using the 901 atomizer would be to explore the MODDING area of the forum. there you can learn to make your own long lasting batttery
mod such as the nico-stick or the magnum
mod. (thanks to nico and madog for their 'ópen source' instructions)
most 510
batteries are sealed to prevent liquid from entering the battery which seems to be the major cause of battery switch failure.... but there are still some unsealed 510 manual batterys but very rare