Stanford Letters of Rec Question?

https://admission.stanford.edu/apply/transfer/evals.html

The website states two academic references + ONE optional for transfer applicants, either professional or personal. I have the two academic references. My professional reference available is the Dean of Students who serves as my advisor in the position of student body president (which is a paid position at my college). Other than this, I’ve worked freelance, so I don’t have any past supervisors for any notable length of time. My uncle/aunt/cousins are (very passionate) Stanford alumni, though I don’t think it would be appropriate to ask any of them as relatives for personal letter. I’m sure I could think of some other connection to write a personal reference though.

Help me out - which category in my case do you think would be the strongest? What are some examples of strong candidates to write a personal letter?