Apparently Microsoft has no plans to fix this

https://connect.microsoft.com/SQLServer/feedback/details/700197/ssis-catalog-doesnt-have-option-to-give-read-access-to-ssis-catalog-to-view-package-run-reports

This Stack link has an alternate workaround

http://dba.stackexchange.com/questions/78341/permission-to-view-execution-report-in-ssis-catalog