How to add fake CSV column names to custom importexport models to make them validate on import?

Question

I have created an importexport module for csv import for a custom model. This module is to support CSVs supplied from multiple sources, so are not all marked up the same. Generally, this is not a problem as long as the correct table column names are used in the right place.

The problem arises from a number of the CSVs containing two, or more, lots of data for the item, depending on the state of the existing items.

Is it possible to specify "valid" column names in the importexport models that don't exist in the custom table? I want a way to add custom column names to the CSV, at which point I will filter the data and break the single rows into multiple, valid rows with the right column names.

For example, here is the first-row of a CSV I have been given:

Afghanistan, 12.5, 160, 13.98, 143, 16.88, 59, 30, 18.88, 53, 26

If the item in the database has a price of £20, then I want the data from columns 1 and 3. For all other values, I want the data from columns 5 and 7. (And in all cases I want the country name - column 0).

As I have said, I want to add custom column names to the above, for example "20rateOne":

country,20rateOne,,20rateThree,,rateOne,,rateThree,,,

My importexport entity models extend Mage_ImportExport_Model_Import_Entity_Abstract.