As often as possible, encourage mentors to hop on voice and/or video chats with the hackers seeking help.
Create a Discord user role for mentors and 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. Creating a Mentor a user role on Discord will allow hackers to see which mentors are online at what times. You can take this a step further by creating roles for the skills and technologies that each mentor feels comfortable mentoring on.