While bankruptcy courts follow the federal rules, many courts also have their own "local" rules regarding forms and procedures. In general, you can file your request for a waiver with your papers. Depending on the court, your request may be immediately granted/denied (if granted, the court will file your papers) or you may have to wait for a decision (the court will usually take your papers pending the final decision). So you should probably complete the request for a waiver with the papers and submit them to the court. But be sure and learn what the local rules are for future filings and become familiar with the required forms of that court.