You can tell them what mindset they should have, and you can tell them to push themselves. Instead of you watching over them, it's their own will to get better that will continue to tell them to push on. Providing maps, tips, habits, etc. in a thread that you would provide to a player 1 on 1 would still work. Maybe not as well, but it will help. Assuming your 1 week S ranking insanes claim is true, a guide w/o a mentor could get them S ranking insanes in about a month. That's still huge seeing most players that have been on for 6 months + have just started getting comfortable with insane maps.
Also, if they didn't want to push themselves on their own or with your help, they could say "f*** it" and ignore everything either way. With or without a mentor, as long as you are online with your training, people will ragequit at the same time, due to the same things.