You can have it positioned over the first option by setting the uicontrol Value parameter to 1.
If you also want it to take the action that would be done when the first entry is chosen, you have to call the callback yourself, such as
handles = guidata(gcf);
popup = handles.popup1; %use formal name of popup after "handles"
cb = get(popup, 'Callback');
set(popup, 'Value', 1); %choose first option
feval(cb, popup, []); %execute the popup passing the object and an empty event
