Glad to see that few of us are now raising it. Spoke to Qlik Support few months back on this. I got response that box plot doens't have it, on my request feature request was raised but not sure when it will be implemented.
Wladimir de Masi (QlikTech)
I checked it here and there is no plan to implement this in the near future.
I created a feature request in my system in order to let my developers know that you are requiring this feature in the system. The feature request ID is 1607.
** How feature request works: We have a system to create new feature "ideas" to our developers. Every time a new customer contact us requesting the same feature as you, this "idea" gets a vote, and the most voted ideas are implemented. **
Another thing to try is commenting in the following post on community, and see if Arturo could help us with this development question.
Please let me know if I can help you in anything else.