Hello Peter,
Not easily with the current version of Hauptwerk, I'm afraid. However the forthcoming Hauptwerk v2 has adjustable tuning and temperaments.
However, a gentleman called Martun Dümig has written a small utility program which can retune Hauptwerk samples. See:
http://forum.hauptwerk.com/viewtopic.php?t=265
I haven't actually tried it, but I believe it should do what you need.
Martin.