The best way to use a Segway, if there is one.

It's the perfect addition to your sheet ghost costume.  Think about it, you can get that smooth, floaty, gliding movement without having to wear roller skates, rig some sort of pulley system, or create an anti-gravity machine.  The only potential problem could be that you look like someone under a sheet driving a Segway, but you can probably avoid that by wearing an umbrella hat under the sheet to get the proper width.  One word of caution: don't snag your sheet on the tires, otherwise, you'll look like a ghost that was run over by a car (unless that's the look you're going for.)