Clean the rotors with alcohol or acetone. Torch them for a few seconds with a flame to burn off the mineral oil. Sand them down with a fine grit sound paper to rough up the surface.
For the pads you can just torch them and sand them and they should be useable again.
Re torching the rotors & pads - would a heat gun provide a similar benefit?
I'm guessing no - as you need the flame to consume the organics in the mineral oil, but as I dont have a torch / do have a decent heat gun - it'd be useful to be sure.