OK - have you already made these assignments? Because if you haven't then why not make them as a quiz instead? Two questions: (1) true/false "I have submitted this work" and (2) essay type where they are allowed to upload work.
For question (1) give this question AND THE QUIZ whatever number of credits you want - eg 2, or 5
For question (2) don't give it a grade. You said grading of the work didn't matter anyway.
Then as long as they answer "true" to I have submitted this work they will get the required number of credits for that item and you can then do any further grade calculations to get their totals.
But if you are using Moodle assignments I dont know how to automatically give them a grade.