You have to move it offscreen as tnl suggests or something (eg, hide it off the edge of an lsbox). I don't think the vwm even keeps track of focus changes while it's hidden. (technically it never does, but window z-order change is pretty close)

I'd recommend the coordinates $allRight+1$, $allBottom+1$, with suitable defaults for allRight/Bottom.

And come to think of it, VWMOnRepaint will also happen when the focused window changes size or position. If you only want focus, you'll get some extras.