Suppose you have a CSV column 'SOURCE' which you want to use for several fields in Drupal. This is how this can be done.
SOURCE -> Temporary target 1
Blank source 1 -> field 1
Blank source 2 -> field 2
The order of the mappings is important.
You can add as much Blank source * as you want. Just make sure it starts with 'Blank source ' and all is well.