If you are willing to try a plant that acts like an annual, try a Mandivilla like 'Alice DuPont'. They seem to do well with full sun, bloom all Summer, and don't get too tall in one season. Some people put them in large pots, so they can be cut down and overwintered. For several reasons, I find that impractical, for me.

Morning Glories are an option if you want to use anuals. You can mix colors and sizes so you have top to bottom flowers. I use them on an arbor. If you put mulch around the post you shouldn't have any volunteers come up the next year.