<p>If you don't care about the credit, I would recommend (as would a few professors) just not signing up for the class, getting their schedule, and just showing up for the lectures you're interested in so you don't have to go to every one minus the number you can skip.</p>
<p>Note: I don't know what the extra time is for (it used to be shorter than that) and it might be a lab portion where you would need to be registered. Find out and then read my advice.</p>