Depending on what statistics you are collecting you may be able to use an aggregator instead.

Otherwise, prior to the statistics calculator you can extract the geometry to an attribute, ensure this is one of your group by attributes and rebuild with the geometry replacer afterwards.

Probably you use the Summary port. If you want the geometries then you have to use an Aggregator (with the same group by) and a FeatureJoiner to add the summary of the StatiscticsCalculator to these geometries. Good luck!