Capture the Path on mousemove.

canvas_mousemove_path.js

'mouse:move': function(event) {
if (mouse_down_status) {
  var grouped_path = [];
  var points = canvas.freeDrawingBrush.convertPointsToSVGPath(canvas.freeDrawingBrush._points);
  points = points.filter(function(n){ return n != ' ' });
  points.map(function(e, i) {
    if (typeof points[i] == 'string') {
      points[i] = points[i].replace(/ /g,'');
    }
  });
  points.map(function(e, i) {
   if(typeof e == 'string')
     grouped_path.push([e]);
   else
     grouped_path[grouped_path.length - 1].push(e);
  });
}