It is possible to craft a CSV file that can be imported... the hard part is actually then creating the spec file needed by the importer to map the CSV fields properly.
This topic on UBBDev is a bit out of date, but will give you an idea of what you'd need to do.
That manual entry option isn't looking so bad now, is it? <img src="https://www.ubbcentral.com/boards/images/graemlins/smile.gif" alt="" /> Do be warned that if you do it that way, from the control panel, only one user can create other users at a time.