By talking with developers of the project! All it takes is a few conversations to get an idea about the why/what/when/ about a project and understand enough of its internals to be able to articulate those same things to others.
Numerous other things can be done by people who don't write the actual code:
* Writing a great "Getting Started" guide
* Writing great conceptual documentation
* Acting as a community moderator and squashing vitriol
* Acting as a contact for companies needing work done on the project
* Keeping things like Github Issues fully tagged, organized, and traced back to from Pull Requests
That's just off the top of my head. There are likely many more things that an OSS project would value which someone who isn't writing code can do.
That said, I'm not sure where you're going to find these people. Good managers are probably getting good manager jobs, and likely don't have the time to hand-hold another community. Combine that with the fact that their power mandate will be less clear in a community, and I doubt you'll get many people that want to get involved in this way.
http://dangerouslyawesome.com/2014/04/community-management-t...
The TL;DR: encourage participation even above solving other people's problems for them - lead them toward helping themselves and others.