Per the USC Admissions Hang-Out Videos on youtube.com, applicants can have extra materials that they deem critically important to be considered by the Admissions Staff sent in to admscan@usc.edu
The sender should include the applicant’s full name, date of birth, common application ID # and/or USC ID #. Anything sent to that email address will be scanned and then attached to the applicant’s file.
Alternatively, you could use this link: http://admission.usc.edu/findyourcounselor.html to locate the admissions counselor for the applicant’s high school/area and send it to him or her directly. But the general email address above may be deemed less intrusive.
I would just not recommend overwhelming them with extra’s. Just keep in mind that they are reviewing 50K+ application files.
Good Luck