On camera modifier for event coverage,

I am going to be covering a Christmas party for someone Saturday and I am wanting to know if there is something that can help the light.

I am use to having the flash off camera but in tis case I will be way to mobile for that here( there will be about 300-400 in attendance). . The party will be at night. indoor outdoor 50/50
The inside ceilings are about 14' and white, walls are all beige,
Lighting is an incandescent light and mostly recessed ( flood style bulbs).
Outdoors will have enough Christmas lights to land a plane but I am wanting some softer light for the faces and I will be using rear sync at slow speeds to allow all natural light to blend.
If you name specific products please include links if you can. The flash is a SB-900

Thank you alll for any input

Demb flip-it would work: http://www.dembflashpr​oducts.com/flipit/

I agree on the demb flipit, or a lumiquest big bounce perhaps. The nice thing about both of these is that inside you can use the ceiling to bounce with a little kick from the bounce device, and then outside you can adjust it to get more forward bounce from the card.