The trick is to get the nose bits in first. Then the rest of them you do buy stretching the frame from the nose. So start at the nose, do the next tabs left/right, then the next ones etc. Much easier.
Putting the frames in luke warm water would be ok as it will make the plastic/rubber more pliable.
Lenses shouldn't be affected at that temperature but, you will damage the thermal part of it, by getting water between the 2 lenses.