Hi muser, I think you may be able to use transcription to do this (setup / usage / importsexports / transcribe import)

Basically you define the transcription table number (a number you make up to identify the record), local code (the "100", though note you don't need the quotes in the screen) and the external code (the "") .

Next you go to the import template, and on the field you are trying to default, scroll over to the TABLE field and enter the transcription table number you created in the first step.

If you're lucky enough and you don't have multiple tables to import into, then you can put all these fields at the end of your import definition and then don't include those fields in your import they will default without having blank columns in your import file. If this is your situation and want more info let me know.

If you have problems let me know what particular challenges you are having and perhaps a screengrab of your import templates Header and Fields.

Hope that helps