Some Rodgersia are hardy to zone 4 and many to zone 5 (if maybe you have or can make a microclimate in your yard these might work). They have large leaves, some are colored similar to the castor bean you are trying to replace, and some have a similar height. If you don't find anything else, this might be worth a try.

I love baneberry, but have young grandchildren, so for the time being make certain I remove all the flowers, and thus temptation. The berries are so beautiful that I can't bear to destroy the plants.

How about ornamental corn? zea mays japonica?
It has pretty multi colored leaves.
Caroline

Is this area in the sun/shade? Do you want to have perennials or annuals? I found Angelica to become invasive after several years-make sure you remove all the seed heads helps also.Mine spread thought their roots into the rest of the bed , under apath walkway also into gardens that were father away.
Have you thought of using several varieties of canna lilies.
Take care Lois

How about a black lace elderberry? I just put one in, after having lived for a few years in zone7 where I had some beautiful small Japanese maples. I'm too cold for the Japanese maples, but the black lace elder made it through the winter. Another idea may be a purple smoke bush.

Not sure about the emplacement, but how about Verbena bonariensis? Grows to over 5ft tall (perennial in zone 9, but I've planted from seed in my zone (4) with no problems). Full sun required. Lovely blooms well into fall.

or... Cotinus coggyra (I believe it's smoke bush?)
or... if full sun, tall sunflowers?
or... another annual, Nicotinia sylvestris alata (the tall perfumed and big-leafed species)
or... any of several varieties of Weigela. I personally love "Carnaval" variegated, creamy two-toned pink flowers practically all summer...

There are several ornamental forms of Amaranthus.
Also hibiscus acetosella has red leaves.