According to http://books.zkoss.org/wiki/ZK%20Component%20Reference/Data/Listbox#Mouseless_Entry_Listbox when using [CTRL + UP/DOWN] the line focus changes.
Technically it works, only the visual feedback is missing.
So you have to blindly navigate to the desired node, and when pressing [SPACE]/[CTRL + SPACE] you finally know which row had the focus.