Thanks, Manuel, for the suggestions.
As it is now with OJS...
1. When the layout is completed, the editor does notify the author by email that the galleys are ready to be proofed.
2. The author logs in, goes to the Editing page, and clicks on VIEW PROOFS (which downloads the PDF, just like the example that you sent us)
3. The author adds any corrections to the Proofreading Corrections box on the same page.
It seems very similar to me to system you sent us,
Public Knowledge Project
University of British Columbia