Take a piece of the milky plexiglass, cut it to a good size so you can velcro or rubber band it on to the flash head. Drill a few holes in it to allow some light to go up to the ceiling and bounce down, while most bounces forward. Tilt the head to about 45 degrees.
Most of the times for wedding receptions and indoor dance type stuff, I'd just use ASA 800-1600, about 1/4 second and direct flash to blend it all together. My Gary Fong didn't get much love from me!