Consider please following pseudo code for using r:dataScroller:
When the bottom scroller is changed, then the top scroller is as well, because the bottom one has render attribute set correctly.
It would be IMHO nice addition, if this had been done automatically. The r:dataTable may know which scroller is bound to it, and update it automatically.
Lukáš Fryč idea for general implementation:
Support for it does not exist in JSF/RF right now. But it can be added. If you have render="A", then also X would be rendered, where X are all transitive dependencies, which make the component. A component can have an interface, to which you can register those explicit targets. Datascroller would use such interface.