Actually I created this widget for my blog a bit before and I too use it. You can see the invisible widget in action by hovering over the area below the Facebook Like Box on the right sidebar. You may see that the cursor pointer changes there on hovering.
To add this widget just follow the below given steps.
Adding the Alexa Widget
You are done now. Now you and your visitors will NOT be able to see the alexa widget in your blog and hence it will not create any layout problem.