Just find a volunteer organization and get an email/acceptance letter for volunteering with them with the letter head of the organization. Also, provide a brochure or printout from their website about the volunteer work you will be participating in. These were the core parts of my application, and I was approved.
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Application Completed By: Me | Date Application Sent: 8/15/12 | Application Sent To: Chicago Lockbox | Mailing Method: USPS Express (Overnight) | Date Application Received: 8/16/12 (Signed for by John Child) | Date Application Accepted: 8/21/12 | Biometrics and I-797C Rcvd: 8/27/12 | Biometrics Appt: 9/13/12 | EAD : 9/25/12|Location: NY