I did some more snooping around and found
unlocking-files-that-are-in-use. The article actually mentions unblocker and shows how to unlock a file with Microsoft's Sysinternal process explorer tool. I don't know if there is a command line interface to this or not, but looks certainly like something worth more investigation. I presume that your company would not have a problem with freeware from Microsoft's technet.
I still was not able to find the underlying mechanism that these folks use to perform the unlocking - but evidently enough folks have figured it out that with more effort, this could be discovered. I hope that the above tool can be controlled via command line and if so, then I think you are in good shape.
