Migrating from Crystal Reports Charts using TopN and "Other" to Reporting Services

I am currently migrating several Crystal Reports that have charts.  The chart series is set to use the TopN values in a count, and combine the rest of the series into one series titled "Other".  I see how to filter the chart using TopN, however I need to still show the rest of the data grouped as "Other".  I think the solution I need is to create a group expression that uses some sort of IIF function to create the "Other" group, but I haven't found a function that I can use to get the results I need.  Any ideas?

We were looking at report deployment options and evaluating SSRS vs Crystal Report Server.  There were several reasons we decided to go with SSRS:
Cascading Parameters
Ability to use multiple data sets in one report
SSRS seemed more user-friendly than CRS
There were a few other considerations I can remember now, but the final reason was price.  My company already had the licenses for SQL Server.  However, even if that was not a consideration I still would have gone with SSRS.
Hope this info helps.