It depends.
In BO Client, you can use the outline feature to "fold" up the detail and only show the summay. There is nothing like this in WebI.
If you have things (like percentages) that require the detail in order to calculate, then there is nothing you can do.
If you simply don't need all the objects, you can simply remove the unwanted dimensions from the block and the measure will roll up as define in the universe.
Steve Krandel
Intuit