Custom button in Reports Module

Hi all, I've seen that there was a similar question asked 2 years ago with no response.
Now I'm here with the same question: how to adding a custom button in reports detail view?
In particular I want to put an "XLS Export" button just below "Export" button in Detail View. A workaround is to insert button in /modules/Reports/templates/templates_reports.php but it's not a best practise of course.
So which is the way for doing this in a upgrade-safe mode?
Thank you.

Adriano