Cocoa Accessibility API: Hide a window

Cocoa Accessibility API: Hide a window

I'm looking to hide a window on OSX (not belonging to my app), but not the
rest of the application. I have tried simply moving the window off the
screen (like I would do in Windows), but the api always positions it at
least 20 pixels away from the edge (#annoying).
Other things I have thought of:
Setting the opacity of the window to zero (can this be done?)
Minimizing the window, but it appears that the window handle becomes null
once the window is minimized, so might be hard to get back
Setting the window level (i.e. desktop) or z order (can this be done?)
Moving the window to a different workspace (can this be done?)
Does anyone know of a way to do this?