I would think something flowing, in a dressy fabric, with an appropriately dressy top, could work. There are certainly formal pants that would be appropriate for a semiformal evening wedding, which I consider about the same dressiness as pref.
For example:
http://shop.nordstrom.com/S/3033848/...bo=6018895&P=1
(I realize those pants are retardedly expensive, but the style seemed right.)