Grasp the dowel in front of your hips, with a very wide grip. Then, keeping your arms straight (no elbow bending!), slowly lift the dowel up and out, arcing it overhead and all the way behind your body until it touches the small of your back. Reverse direction and return from back to front until you’re in the start position again. Take it slow and be gentle. No jerky movements here. Push the dowel out away from your body as you rotate through, as if you're trying to lengthen your arms and get the bar as far as possible from your head.
The roll-through should be smooth and controlled. If you're bending your arms or having to roll one arm through at a time, your grip is too narrow. If you can move through all parts of the motion easily and symmetrically with straight arms, narrow your grip an inch or so on each side and do a few more reps. Repeat the narrowing process until you find your sticking point. Then practice dislocates just outside that width.