Ask HN: Strategies for mentoring junior developers remotely?

Mentoring junior developers a normal office environment[1] is one thing, but I've found it much more challenging to do so remotely. You can no longer slide your chair over, pair and work through problems as easily, and it's much harder to teach (or be taught) over Skype et al. Communication in general is more formalised, and harder to read intention.

What are some good, holistic approaches for helping train up-and-coming developers all the way to “senior developer” skill level, while being fully remote?

[1] https://news.ycombinator.com/item?id=16707059