The default is no offset for any pie slice. If you implement one of the following datasource methods, you can provide offset values for any or all slices. Return zero (0) for a given index to indicate no offset for the corresponding slice.
-(NSArray *)radialOffsetsForPieChart:(CPTPieChart *)pieChart recordIndexRange:(NSRange)indexRange;
-(CGFloat)radialOffsetForPieChart:(CPTPieChart *)pieChart recordIndex:(NSUInteger)idx;