A colleague found a simpler way, using Preview. Open the pdf whose metadata you wish to change in Preview. Then, select Print, and from the print menu, choose the "PDF" button in the lower left corner. Select "Save as PDF". The window then offers you a chance to edit the author name. If you set it to blank, then that field does not appear in the metadata (as verified by selecting "get info" in Finder, and by examining the document properties in Adobe Acrobat.)
It is unfortunate that this option is not present when you export to PDF from Pages (etc), but at least it is doable using only standard Apple programs. Though I have no way of knowing if this is as thorough as some third party programs and services.