Thank you so much for your response!
29 pages double spaced, 12 of which include results and discussion (the sections he most wants to review).
STEM (biomedical)
I have incorporated all the feedback from him on the sections we did live editing on. I have also incorporated the feedback from my other readers in the lab so the draft he has is a revised draft. He hasn't read any draft of it at all, so I'm unsure how highlighting the changes would help him. Most of the other people in the lab have suggested smaller changes, things like grammar and small sentence-level changes, nothing substantive to the overall organization or message. I have suggested summarizing the sections so he doesn't have to read as much and can focus on big picture editing, but he refuses and says he 'just needs to sit down with it in a quiet place and read it through, really focusing on it'
I did attempt something like these action items in the form of a calendar which I presented at one of our meetings. He agreed that it seemed reasonable (included things like deadlines for him to give feedback, a planned submission deadline by the end of the month, dates for me to have the cover letter to him by, etc) and I sent it to him via email after the meeting. We've missed the first deadline... I've tried deadlines before (and getting him to agree to read a section of the draft before our next meeting). He agrees enthusiastically. I check in halfway through to the deadline and he says it won't be an issue, then the meeting/deadline happens and he regretfully says he hasn't had any time to read it.