How can I mute Assignment Comments in SpeedGrader?

I give comments on ungraded assignments using SpeedGrader. Last year I was able to mute an assignment in SpeedGrader, upload my comments at my own pace, and then unmute the assignment so all the comments were visible at the same time.

Now, it appears that there is no way to mute comments, just grades, using the New Gradebook. I have my Gradebook set for manual grading. Am I missing something?