Can a lightbox be locked?

Hi all! I have a question for anyone who might be able to give me a hand. I have a situation where I there are things on a slide that need to be completed before advancing. In this case the slide in in a lightbox. I don't want the user to close the lightbox prematurely. There is a button that will appear on the slide at the right time that will execute a couple of triggers and then close the lightbox.

So, can that little red X to close a lightbox be locked in some way?

I would have simulated the lightbox effect but I don't want users to be taken to another slide. I want them to have the ability to remain where they are, view and close this material, and still be able to use the back button to logically backtrack their steps.

Thanks!

Stephanie