Captivate 8: How to add a button onto a question slide to invoke some java script?

I have some question slides where the user has to guess an item on a picture. Because the picture is very small, I want to add a zoom button which calls a function in my LMS to popup the picture in a bigger window. I could not find a way to add a button where I can call java script, so I tried to solve this by using a smart shape with option "use as button" set and adding the java script action. This works fine for the popup but now the submit button on the slide no longer works. Clicking the submit button just disables the answers and stays on the current slide even if I did not click onto the shape button previously. How can I achieve my goal to display a bigger picture of an image on my slide on the users request?

I also tried the "ImageView" widget, but this is not a practicable solution.

Thanks,

Martin