Not being flip but the best way to make your speakers disappear is to close your eyes or turn the lights out. Experimental psychologists have studied the "ventroloquism effect" which is a tendency for the perceived direction of sound to be where the source appears to be, not necessarily where it is. As long as you can see your speakers your brain will be fighting this tendency. This is probably one of the reasons why headphone listening can give such good localisation, nothing visual to distract the ear. Of course it helps not to have phantom channels and room reflections messing things up too.
Speakers "Disappearing"
I have read a lot about speakers "disappearing" so that one can't tell from where the sound is emanating. But, what about all the stereo tunes where the recordiing engineer intentionally pans the music to come from one side or the other? Can the speakers be made to "disappear" in that situation? Or, is it just the nature of the particular recording?