As often as possible, encourage mentors to hop on voice and/or video chats with the hackers seeking help.
Utilize a #mentors channel for folks to post when they need help and encourage your mentors to keep a close eye on it. Since you aren’t asking anyone to travel, you can recruit mentors from all over. Invite alumni from your school, industry professionals, and your professors to join during shifts throughout the event. Keep a live document of what mentors are online at what times, along with the skills and technologies that each of them feel comfortable mentoring on.