I heated up the inside with a hair drier on hi (I think a heat gun/paint stripper would melt the thing if you're not real careful), then put a towel on my head, jammed the bucket on grabbed it both sides at the bottom of the earpieces, pulled it down real hard (to make the top a dome instead of a shelf) and pulled it out to make the flare.
Stand like that for as long as you can (in front of a mirror is good so you can a)see how much flare you're getting, and b) realise how much you're suffering for your art). When it's cooled a bit, take it off the plunge it in a basin/bath of cold water (prep the water first, natch).
The results on mine are passable and they have stayed put so far (a few weeks), although I have yet to carry out the visor surgery. I figured it'd be better to play about with the shape whilst it was still in one piece, then once I was happy with that, re-do the visor.