1 pvc slip t-connector or a short ridged tube that fits the dowels
2 round dowels
2 broom holder clips
Mount the holder clips to the easel's top canvas support. I found these broom holder clips in the home organization section at Walmart. Clip on one of the dowels then slide on the pvc connector. Rubber band the second dowel at right angles.
The pvc allows you to slide the mahlstick horizontally and the rubber band allows you to slide the verticle stick up and down to adjust for different sized canvases.
If you wanted to spend more time I'm sure you could come up with something better than rubber bands, but I'd rather be painting.