power view permission on sharepoint

Question

I have a power view report deployed to a PowerPivot gallery on Sharepoint 2010. No one had access to it, so I created a group and with read permissions on this site colection like this:

now, as expected, the users belonging to that group can see the report. But the "edit report" button is available. Even though they cant save the report, I would like to disable it. How can it be done?

Thanks