How about a hydrangea? More a bush than a tall flower - check out the Hydrangea Forum since the verdict is still out over some of the newer varieties, like "Endless Summer", etc. Or a Black Eyed Susan, the Rudebeckia Goldensturm variety can get pretty bushy and high in a growing season. Or... let Morning Glories or a Clematis climb over the evergreen.

Great ideas! Thanks. I especially like the climber suggestion. That would really fill in the gap.

Queen of the Prairie, echinacea, Joe Pye weed, cleome (annual).

Hallo,
here's a idea, Dahlia, the ones I have tried so far are all big bombastic, with a abundance of foliage & flowers that just come back over again, they keep going until freezing temps when you can choose wether to dig up the tubers & save for next season or not, it has worked real well for me to plant the tubers in place of a newly planted perennial that needs a few seasons to look their best, mainly clemmies ..
I really looks wonderful when they go, 7 the benefit is that dahlias goes in to full force in terms of buds when most flowers are done for the season, namely late summer early fall.
Best of luck.
Kerstin