- overwrite the method angle.getLabelAnchor() which returns a JXG.Coords element
- Apply the moveTo() method once. This is a dirty hack, but it seems to work, see https://jsfiddle.net/m7r6o2jk/2/
var a = board.create('point', [0,0]);
var b = board.create('point', [3,0]);
var c = board.create('point', [1,3]);
var angle = board.create('angle', [b, a, c], {name: 'α', radius:1});
angle.label.moveTo([2,2]);