EI 14-3 is pretty straight forward for one Star. You just need to have control over your bankshots. You can use the Aiming Help Pic above to adjust your own aiming. The yellow line is a real shot and the red dot in the picture is the lowest position on the left side of the pole where you can keep your pointer without hitting a Doom Skull.
Save a Rainbow bubble to drop the Doom Skulls by banking the RB Bubble up left after you have gathered a good amount of yellow spiders and perhaps some green to drop them on.
Level Design Pic made with the Charm of Scrolling here.