Got it! Makes sense. Not ideal, but what about uploading the file and then having them paste the URL in the comment box?
Actually, the student can submit multiple times. It's actually unlimited. So they would upload files the first time and hit submit and then they would upload the URL the 2nd time and hit submit.
For the instructor, you can toggle between each submission in SpeedGrader. I use this feature all the time.
HOWEVER, unfortunately, even after YEARS of people begging for it in the community, students are only able to see the LAST submission and if you put comments ON any of the other submissions, they will not be able to see them.