Try this if it's too sunny: position a small Fast growing tree such as vitex agnus castus in such a way as to provide afternoon shade. (I know you say southern exposure but really watch the sun this year and figure where shade falls around 1:00 in, say, July.) The vitex is a pretty little tree that won't get too tall and has neat ornamental appearance for a front yard. In your zone it might die back or be cut back to ground each winter and remains small no more than 4-5 feet. Big enough to provide shade for a peony. Plus after peony flowers are gone in mid summer vitex is covered with beautiful blue lavender flowers of its own.
Also in my zone peony foliage dies back completely and can be an eyesore in mid late summer so behind the peonies I plant lantana (perennial here, annual for you) which comes up after peonies have bloomed, the lantana needs hot days to really take off, and when it does it explodes covering the dead peonies.
Just a few ways I grow peonies in "full sun" in the South.
