You can use the csv upload to separate your users into cohorts which might serve your needs.  You need to create the cohort/s first and then add a column cohort1 to your csv file and add the numeric id of the appropriate cohort.  Then go through the upload user process but make sure that you have Update Existing Users selected.  If you don't have your users in an excel/csv file, use a utility like Adminer to export the info directly from the database.