I'm still a little hazy on the plumbing details of all the bits and pieces of IndieWeb but I would have thought that if withKnown has a micropub endpoint and micro.blog can send to the WordPress endpoint, it ought to be able to send to WithKnown. But I'm probably exposing my ignorance. And maybe it is on the roadmap.
I seem to remember mentioning something like this to Manton in the first week out of the gate, so I know it was on his radar, but perhaps hadn't been documented in his issue queue to support directly as that came during the second week sometime.
Chris Aldrich, Oct 23 2017 on stream.boffosocko.com