If you can get a friend to go to the parking office for you, there is a machine in there that, IIRC, can be used to pay off tickets, excise tax, and the like. I think all you need is the citation number and a credit/debit card (can't remember if it takes cash). Alternatively, someone could probably wait on line and give cash to the people in the office as long as they had the citation number (and maybe your plate number as well, just for extra confirmation). Know anyone who's willing to front you $20? :-}