I know one way to do this , but only if the hours in your expression is not a Sum().
If your expression is just [Hours] you can change this to AVG[Hours] , this will return the average on every line but this will be the same if you don't use a calculation in your expression (fe: AVG(10) = 10)
So this way you have the right hours in your expresion.
Now go to the tab Presentation and now check "Show Partial Sums" for Employee Name.
Hope this works for you.