It's a shame no one has had a suggestion for you. As far as I know, brugmansia is not hardy (but you can inquire on the Brugmansia forum, of course).

You might want to post a new question with a different title - "looking for late season white blooms". Does it matter if it is a shrub or a perennial? If you're ok with a perennial, then perhaps post this question on that forum instead and note that you need something for shade.

If it gets full morning sun, determine how many hours of sun that is, it may qualify for a full sun plant if it gets 6 hours worth.

if you will e-mail me I will be happy to send you some White Datura seed. I must warn you that the plant can be a pest if you do not keep the seed pods collected.
If you bring your Brug inside each year, cutting the growth for rooting, you should not have a problem at all with it.
I have several white ones and when I learn how to mail them so that they do not decay, I will also be happy to send you cuttings of them. They are so very easy to root. If I can do it, you can do it.
Brugs are another new passion of mine.
merrissandjack@hotmail.com
The Brug forum will be very helpful and TnGreenThumb is a regular expert and will give you confidence.
This is my first visit to this forum..but send me your address and I sure will help you out!

Try the Formosa Lily hardy to zone 5. Also try Cardiocrinum giganteum hardy to zone 6. See http://www.waysidegardens.com/ for both Angel's Trumpet look alikes

Here is a link that might be useful: Formosa Lily At Wayside Gardens.

Is sweet autumn clematis hardy in your zone? It's covered with fragrant white flowers in late summer and early fall. How about anemone Honorine Jobert? White flowers in the fall.

Or moonflower which is a nonhardy, white, deliciously scented morning glory - blooms open in the evening though.