Mapping a file field

Not really answered on http://ww.wp.xz.cn/support/topic/attachments-16, reposting here as ‘original question’:

The plugin uses wp_remote_post, which according to this answer doesn’t support sending files, but according to this hack you can use it if you build the entire HTTP post.

Since it should work with the regular curl, you could use hook #5 to bypass the (what was supposed to be more WordPress-y) wp_remote_post and use curl instead; note that you’d have to format the returned response to match the array normally returned by wp_remote_post.