The quickest and probably easiest way to calibrate the units to g's would be to drop the remote (onto something soft) while collecting the data. If you're careful, you can drop it so it accelerates along just one axis of the remote--I'd recommend just holding it by one end and dropping it. Take the average of the acceleration along the long axis during the drop and, voila, you have a measurement for g. If for some reason you can't get it to drop parallel to an axis, you can square the average of the acceleration along each axis, sum the squares, and take the square root of the sum.
I don't know what the acquisition rate of the wiimote is, so I can't tell you how far you'll need to drop it. I'll try it out next week--I'm going home for Christmas and my brother has a Wii.
Feel free to ask me if you need any help with using the accelerometer data--I'm a grad student in a gravitational physics group.