Set course as complete before last slide

I have a SCORM 1.2 course with 50 slides. Ten of them are extras with optional information and not something users are required to view.

When the user gets to slide 40 I need to set the course as completed but I'm unsure how to do that.

The publish settings allows for user access, slide views, or quiz:

- To set it as 'user access' would mean, I think, that as soon as the user accessed the course it will be marked as completed.

- 'slide views' could be set to 40 x 100 / 50 = 80% but if the user viewed some of the extras then they could be deemed as having completed the course without having got to slide 40;

- 'quiz means I need a quiz but there is none.

Should I just make a JS call at slide 40 to set the completion status?