So, that is what you do. If the Joint Sponsor is employed, include either the tax return transcript or (if not yet available) a complete copy of their federal tax return, including all schedules, W2, and 1099 forms. Also provide a recent pay stub. If self employed, it's unlikely there will be any pay stub.
You mentioned a 1040. That's not a complete tax return for everybody, but even a 1040 without W2 and any 1099 forms is "incomplete".