Yes the string was my method too.I've never seen on like that, as a top ring, our rings were metal slabs, apart from the grill, which used bare wire. To rewire them, you didn't 'stretch as you went' - you measured the length with string, then stretched the element to match the string length, so it was nice and even once in it's slot.
That sort of arrangement used to exist in in ceramic/glass topped hobs but more recently it's rigid elements.