Part of getting what you want is asking for it properly. There are a few tried and true methods when asking permission from another person of authority. When you're doing the asking in the form of a letter, the best approach is to be both courteous and straightforward. When you follow the format for writing a formal letter, you can politely ask the addressee exactly what it is you need permission for.
Open a new document on your computer and hit "Enter" once to create a top margin on the page. Type "Sub: Permission" on the left of the page to indicate to the reader the purpose of the letter and what the following content will be. Hit Enter twice (once if you've formatted the document to include double spaces) and type "To Whom it May Concern:" or the full title of the addressee. Be sure to include the colon.
Hit "Enter" twice and type the body of the letter, which should include your name in the introductory line, followed by all the pertinent details regarding what it is you're asking permission for. Be clear and concise, giving any dates regarding what it is you're asking. Ideally the body shouldn't be more than five lines long.
Hit "Enter" twice and add in any additional information or thank the person reading the letter for their attention in the matter and thank them for any quick response they may be willing to give. Also give your contact information in this line.
Hit "Enter" twice and type "Sincerely," (with the comma included) and hit "Enter" twice again. This creates a space where you'll sign the letter electronically if you'll be e-mailing it or in ink if you'll be printing it. Type your first and last name and either print the letter, sign it and mail it or sign it and e-mail it to the addressee.