CSV import to default columns?

I imported issues for the first time using the CSV importer. It went well, except that I wanted all issues to have the same Reporter, Task, priority, and value for a customfield. I could not see how to do that except to create a new column in the spreadsheet and populate it, which was a manual effort. Is there a way to set these in the configuration file nexttime I need to do this? I realize it is (probably) using the system default for undefined fields, but is there a way to set the default for a particular import session?