1. Add a key position key frame on the frame after the squash frame.
2. On the key you just added, reset the x, y, and z scale to 1 in the channel box. Now use scale to stretch the ball on this frame. Remember to keep the mass of the ball constant.
3. Rotate the stretched ball so that it follows the motion arc.
4. Add a rotation key at the apex continuing the rotation you established in the stretch frame.
5. Add a rotation key on frame 1.
Whew, have a cigarette.