The real problem here is trying to associate the iclickers with the correct students. I found last term about 90% of the students were fine, but the other 10% were very difficult to handle:
The problems can be solved by either having the special registration session for problem students / clickers, or by having a normal session with a small number of students, starting a question and having up to 5 of them answer A through E on the iclickers. Ask as many questions as needed to get data for all the problem students / iclickers. The iclicker numbers can then be read from the ".raw" file in the MyCoursePC/SessionData directory. It will have iclicker numbers and responses. These special .raw and corresponding .log files should then be deleted or moved so that igrader does not try to grade them later.
Once you have associated the correct student IDs and clicker numbers, edit them into the file MyCoursePC/SessionData/RemoteID.csv. Remove any duplicate entries for the student or clicker. Igrader uses this file to associate clicker with student.