I realize you asked this in August 2013, but in case it still helps you or others, as of Feb 2014, SQL Developer has an OLAP extension which seems to be what you were looking for...
The OLAP extension enables you to use the familiar environment of SQL Developer to create and manage dimensional objects in Oracle Database 12c Release 1 (12.1.0.1.0) or higher. Oracle OLAP provides advanced multidimensional analytic capabilities and storage within the database, including excellent query performance, fast incremental data updates, efficient management of summary data, and rich analytic content, such as time series calculations and both additive and nonadditive aggregations.