And this is where it helps if the client is a developer. A developer who understand agile processes should be well placed to break tasks down into vertical slices in this way.
On a related note, I highly recommend Trello for co-ordinating with remote workers. I just invite them to a board and send a "welcome" notification to them from a special "Message Card". They immediately get how the whole thing works even if they've never seen Trello or Kanban before, and you can spend most of the time co-ordinating on tasks by messaging on their cards. This is from my experience with researchers/admins and I'm planning on the same for working with a developer.