They should do like the tech community. Make "Pinterest Boys Meetup" and "PiGuys" making free lunch paid by all the major clothing companies where girls are not allowed to participate. Also, they should host conferences and encourage guys to participate and make discounts for them. They should tell everyone how much they appreciate guys joining them.
(Also all of those things would work, if men were negatively affected by our current patriarchy in the same way as women are in tech, which they aren't.)
Fwiw there are some groups like that for men in industries where there's historical stigma against male participation, like nursing: http://www.aamn.org/. Doesn't even seem particularly controversial; the AAMN doesn't generate nearly the level of anger that women-in-tech groups do.
There's no controversy because these goals are always seen through the lens of society as a whole. Groups like the AAMN helps people who are generally privileged achieve parity in an area where they are currently stigmatised. They don't do anything that looks like it erodes male privilege, so there is no reason for them to attract any ire.
