The best method that I've found is to grip the lower half in your left hand, the upper half in your right hand with the screen facing up, and twist your left hand away from you and your right hand towards you. It should start to separate around the LIGHT button.

Once it starts to open enough I suggest working a finger/fingernail into the crack so it doesn't snap shut if you relax your grip. With both hands begin working the case open around the top of the remote and down the side opposite the LIGHT button. The bottom half is a little trickier to separate, so you may need to use a little force - but not too much, it's easy to damage the plastic snaps down there (but don't worry if you do, I've damaged two on my worn out MX-700 after about 8 openings and it still closes tightly).

Once open remember to pay attention to how the LIGHT button and IR shield fit in.