Review Defects: Can we modify the roles so that this option is set automatically or "hidden"

Only show me the "Mark as Read" if my role requires me to take action.

Template rules can change the action required on this button.  

An observer may not have to read.  

The Mark as Read just indicates that you have read the comments.   

Can we modify the roles so that this option is set automatically or "hidden" to the end user when they are in a review and their role doesn't require them to review the comments.