There has been some discussion in the forums about creating reports where Top X values are displayed with all other remaining values displayed as a single 'Others' value. (Grouping specific entity members).
An idea has also been submitted to request this feature.
The purpose of this document and sample is to demonstrate that this is already possible, though it requires a little work.
The attached document contains an example using the standard 'Delta' database.
Caveat: this was created in 2014 using Board 8.1.4. I have not retested it with Board 10, but it should work as it uses standard Board functionality.