I think this would be an excellent feature to reduce fragmentation of seldom changed files. There are certain folders that are constantly changing. For example, the "temp" folders in the user profile and in Windows, also, folders where antivirus definition files are stored. If the files in these folders could be moved to the end of the drive, as these files are deleted or replaced they would not be creating space between files that are seldom changed.
With this feature, each time defraggler is run, the seldom changed files would not need to be moved and only the frequently changed files at the end of the drive would need to be defragmented.