To the best of my knowledge it is not possible to conditionally select the dataset that you'd like to use for a single tablix.

Another solution (to avoid the expression based...

Without further clarification, I am having a hard time understanding what your exact application will be and so I am not sure if I am providing you with the information...

How much detail is included in the details summary?

Would it be feasible to use conditional expressions to select which dataset values are actually pulled from?

You can specify explicitly the scope...