You need to insert a subreport into a larger report using WordWriter.
Generate each subreport separately and then use the WordApplication API to merge the subreports into the larger report. The subreports could be appended to the main report document with Document.Append, or if you need to insert the subreport into a particular place, you can use Element.InsertAfter or Element.InsertBefore.
Flatten your data set and use WordWriter Grouping and Nesting. Grouping and Nesting would allow you repeat sections of a document for a particular subgroup in the data.
NOTE: Both these solutions require WordWriter Enterprise Edition. For more information about the features offered in Enterprise Edition, check out the OfficeWriter Change Log page.