This happens a lot already. In terms of mentoring other mentors, I think the easiest is just setting up phone & email correspondence between people that can help eachother out. When I was running 1511, I helped several other rookie team leaders this way, they ranged from mentors a few towns away, to mentors in CT and even further sometimes. They had my email address (and I was generally available within the hour), and my cell phone number. I was able to walk them through a lot and answer tons of questions that way and it was very simple.
I agree that if you are virtually mentoring an entire team, more fancy things like video chat, skype, etc can be beneficial. You can show design drawings, parts, etc... but really there is a lot that can be done by email. These past two years since I moved away from 1511, I have remote mentored them in several ways. The most common is just answering emails from various different mentors & the team leader. I even had one of the mechanical guys during build season have me check his motor calculations!! I also spent plenty of time on the phone with some of the lead mentors... talking over everything from initial strategy kickoff weekend to how to run certain meetings, deal with integration issues, etc. But I admit, it was great to be "in" on their early strategy and design sessions via their livestream video & chat. I even helped with some strategy & design suggestions that way!
But I think your idea of pairing up some of your inexperienced mentors virtually with experienced ones can be very beneficial. It gives them someone else to ask and talk over things with, as I'm certain you will be very very busy
The number one thing to remember is that half the time, the new mentors may not know what questions to ask, or when to ask them. Seek out experienced mentors that are willing to poke and prod a little, or maybe set up every-other-day checkins to start.
Good luck!