@NLNOG @marlies This isn't going to be a perfect solution by a long shot either (and they often have their own diversity issues on other axes), but have you considered visiting various hackerspaces and chatting to the people there, to learn more about what would would interest them (or, conversely, keep them away)?
Seems like there *should* be a fair amount of overlap in terms of technical interests, so I suspect that some answers can be found in the cultural differences.