There should be two modules with ReleaseMFD, one mouse controlled, the other MFD controlled. I'm at work now and can't remember for the life of me... But I think you bring up ReleaseMFD, and the MFD will tell you which button on the MFD or which mouse click will do it. Not sure, like I said, it's been a while.
Arc's method works also just less 'immersive'.
There is also a need to be 'in' the ship to be separated, or something...
I know there are a few threads here on the forum regarding this. But I gotta go to a meeting here soon.