This is already there. If you go to package properties and select Reports you will see the constituent reports of the package. Beside each report is a check box. Simply uncheck the ones you don't want to run, click Apply then execute the package.
I see that the checkbox's are already there, but when I have 40 reports and need to rerun 3 of them, it can be tedious, then after I have to remember to go back and recheck everything.