For the dashboard to appear in the selection dropdown it must first be starred. Starred is also not a property in the json but an http action (check the api call the UI makes when you star a dashboard to see what the HTTP call looks like)
If you first save the dashboard via the HTTP API, then star it using the the /api/user/stars/dashbords/:id call, then you can update your user preferences using preferences http api: http://docs.grafana.org/http_api/preferences/