In ZK 8.0.3.1, popupmenus can be opened or closed from server side.
However, there is no API to choose the current active position in the menu.

http://zkfiddle.org/sample/1fn81c5/1-Menupopup-focus
The attached example / fiddle shows the current workaround to open and select a position from server side using javascript evaluation.

It would be nice to have a simple server side API on menupopup such as:
myMenupopup.setActive(Int index);