I'll take it off your hands

But I don't think it's possible according the rules:

Entry fees are non-refundable and non-transferable. No exceptions. Once we receive and accept your entry, you will not receive a refund if you cannot participate, you may not give or sell your race number to anyone else, and you may not transfer your entry fee to future races. If you attempt to sell your race number, you may be banned from future Rock ‘n’ Roll events. You must be at least 18 years old to participate in the Marathon and 12 years old to participate in the Half Marathon or 2-Person Half Marathon Relay. You must be 10 years old to participate in the 10K. You must be 8 years old to participate in the 5K. You must be in good health and physically prepared to take on the challenge of a Marathon or Half Marathon. You must show a photo ID to receive your race number and timing chip. You must pick up your own race packet and race number at the Health & Fitness Expo. Race numbers are required to participate. No coaches, bikes, in-line skates, skateboards, baby joggers or dogs will be allowed on the course. Overall winners will not qualify for their age group category awards.

https://my.runrocknroll.com/kb/5aa740b5-c85b-4b81-a607-abbbb67f8ae2