With SQL Server SP2, Microsoft added an Aggregation Manager utility to its samples. It is not installed by default, and has to be downloaded separately from http://www.microsoft.com/downloads/details.aspx?familyid=e719ecf7-9f46-4312-af89-6ad8702e4e6e&displaylang=en, file SqlServerSamples.msi
This utility allows you to see existing aggregates, and allows you to easily add aggregates manually or from a Query log. Do not miss this one!