can't remove the brake piston

["simon hurley" <simonsensis@hotmail.com>]

Just taken the brake caliper off my 77 MGB.  The pistons are stuck in there 
and screaming "no no, I'm not coming out!!"  Any recommendations for 
enticing them out?  Using the cars braking system to blow them out is a non 
starter like the car.

Thank you in anticipation of your very useful help.

Simon