Forks are easy enough - chop the stem off, take the fork out, and up-end it in such a way to dip the steer tube in a bucket of lye. Three days later, the aluminum will be gone - vanished. Clean steer tube, fit fork back into frame, install new handlebar stem. Finito.

Can't do this with a stuck seatpost though, for lye will ruin the paint on the bike. Only way to do this is if you can fill the inside of the seattube up with lye WITHOUT the lye dribbling onto the paint of the bike. Ain't easy if you have bottle-cage braze-ons (your only hope is to temporarly screw bottle cage mounts in with silicone to seal the gap off), and you still have to worry about the lye leaking onto the outside rim of the seattube lug when the post finally gets eaten up to that point. Then there's the big splash of lye coming out the first gap in the seat tube...

-Kurt