Over on the Radical Redux thread I toyed with the idea that Palpatine used some sort of parasitic Sith 'spell' or power up to save Vader at the expense of the one thing he loved most.

Upon reflection I think it's a bit silly and almost impossible to convey on screen without some sort of expositional dialogue.

Though I can't help but imagine with that brand of cruelty you can only get away with inflicting on fictional characters that Padme burning while Anakin partially regenerates would be visually interesting at least.