You will have to implement the DICE (drop if course exceeds) feature of boss. DICE works as follows:
If a student is allowed to bid for n courses (say 5 course), DICE will let the student bid for an additional course if the following criteria are met
Student has enough credits for the extra bid
After the student selects the extra bid, the system should prompt the student to specify which course to drop automatically if DICE succeeds. DICE is considered to have succeeded if the student is successful with all bid. I.e., the student wins all 6 bids (if the student is allowed to only take 5 courses). In this case, DICE will automatically drop the course chosen by the student from the student’s course list. DICE does not do anything if the students fails to win all the bids.
Bids that are dropped are not automatically filled with the next lowest bid.