Average results slide for completed quizzes only??

Hi all

Ok so i've come across a massive challenge with results slides. 

Basically the course has two sections in where the learner needs to complete any of 4 quizzes. Now this could be all 4, combo of two or even just one. Now that's the easy part. I've set up each to have it's own results slide. However the challenge comes in the client still wants an overall course pass mark. Now when I use a results slide to combine all these 4 possible results slides it gives an average on all, not just completed quizzes. So for example if I only complete one quiz and get 100% - the combined results slide that will report averages to 25% and the learner is still at 0% on the other 3 quizzes.

Does anyone know a way of doing this? Client wants an LMS score so I can't just use the 'complete course' trigger. Even that comes with it's own complications of when does that happen based on the multiple variations of completed or not quizzes. Added a very crude SL project with 2 sections in so you can get a feel or play around with a solution. When I did my test back in November on this I managed it i'm sure in the same way i'm doing now. 

Any help is much appreciated as at this rate it's going to be a complete redesign of the course for the client.

cheers, Phill