If you are using 4.5, you should be able to call setFocus on the button.
This solution does not allow the PopupAnchor to be accessed using a rollOver
I'm not sure I understand the goal. There isn't much point to setting focus
to a button. All you can do is hit space to "click" on it. If you've moved
the mouse to hover it, why not just click on it? It might be easier to
just capture the space key at the DG level and perform whatever action you
want the button to represent. If you subclass DG, you can get access to the
Renderers cannot be given focus unless the DG has editable=true and the
column has rendererIsEditor=true.
Found a solution.
On mouseOver of label set popupAnchor.displayPopUp = true and set the value to false on mouseOut unless the container gets mouseOver.