I just received an iPod HiFi in the post! The left and right speaker domes were inverted and the centre showed signs of previously being inverted. After thinking a while, I decided to wrap my lips around the domes and give a good suck. Both popped back into shape! They do show some crease lines from where they were previously bent but it’s not too bad.
If you try this method, I suggest you brush your teeth or chew a little gum first. These HiFis appreciate fresh breath when you’re giving them a kiss of life.