Thank you to all of you who responded to my inquiry about underbustling a wedding dress.  The dress has an empire seam, not a waist seam, so placing all the weight at the center back seam at the empire seam, or even at the waist, would have created unsightly dragging.  I was able to alleviate this problem with a waistline stay and strategically placed straps and loops.  It took some creative thinking, but the bustle held up through hours of vigorous dancing.  The bride and the sewers (her grandmother and myself) were very pleased.