Storyline 3: How to Mark a Course Complete with a Branching Story in which not all slides are required

So I'm creating a sales interaction simulator in which the learner is presented an objection from the on-screen character, and the learner has to choose from 3 responses. Based on the responses that the learner selects he/she is rewarded with points. Better answers score higher than answers that might not be as good. If they score enough points they move on to the next stage, then, ultimately, complete the course.

I realize that in LMS Tracking I can change the minimum number of slides visited to set the completion criteria, but the number slides that the learner completes could vary, depending upon the answers and the total points. For example, a learner could complete a section and move on with only 3 slides, or as many as 5 slides, if they get back on track.

I didn't create these slides or responses using quiz slides. So I thought I could create a hot spot slide at the end of the course where the learner would click and then be directed to the closing slide, and change the tracking criteria to "Quiz Results." However, whenever I put the hotspot slide the Tracking Quiz Results option is still grayed out.

It's highly probable that I simply don't know how to use hot spots in Storyline. But I'm also wondering if there's a way to use variables to mark the course complete.