No - you are unable to do this. It's roughly along the same lines of a button in it's pressed state when a user clicks it - an 'interim' operation for the user to set a value. You could focus to it, but that's about it.
If you really wanted to simulate this, you could play with some CSS. For example, you could create a list that looks like the dropdown list and set the dropdown value based on whatever the user clicks - similar to how an autocomplete list looks.
You could always change it to a multiple line list box if you wanted to display all the values to the user. You'd do this by setting the size to any value and back to 1 when you want to hide. It's not perfect, but it's another option:
$("#open").click(function(e){
   e.preventDefault();
   $("#myselect").attr("size",5);    
});
$("#myselect").click(function(){
   $(this).attr("size",1); 
});
http://jsfiddle.net/jonathon/cr25U/