dynamically add scripts to WP_Widget widget() method

I am creating a widget with the standard widget code like below

class my_widget extends WP_Widget{

function my_widget(){
   //do setup stuff
}

function form(){
   //do form stuff
}

function update(){
   //do update stuff
}

function widget($args, $instance){
   //how can we dynamically add style and script here

   //this does not work
   if($instance['val'] == 'test'){
      wp_register_script('test', plugins_url('test.js');
      wp_print_scripts('test');
   }else{
      wp_register_script('diff', plugins_url('diff.js');
      wp_print_scripts('diff');
   }
}
}

I am wondering if it’s possible to somehow add scripts dynamically to a wordpress widget… I am guessing that this would have to take place within the widget() method b/c that is the only place where dynamic variables are passed, but the problem is this function appears to be fired after scripts are added.

Thanks a lot for your help on this. My widget is more complex than this and it currently includes atleast 5 scripts on each load that are not necessary b/c the only solution i see is to add the scripts in the my_widget() function, which does not allow me to dynamically add scripts like i have shown above.