[CRM 2011] Import data programmatically with file annotations

I'd like to create a configuration page for our solution which will allow the user to import sample data.

The requirement is that this sample data will also contain attachments (annotations with files). I can do so using a zip file with all the import data inside, but this requires I use the wizard available using the CRM web page.

I noticed that ImportFile.FileTypeCode can be set to 3, which means it's an "attachment", but how to actually use this feature is not documented. I also tried importing some custom sample data using the wizard and then looking at what CRM contains in the data base, but alas, all ImportFile rows have FileTypeCode = 2.

How do I go about importing data with attachments in CRM2011 programmatically?