As a workaround, I could create a dummy file of the same size and ask MyDefrag to put it at the beginning of the disk (as in my first suggestion above). Then I would delete it and use PageDefrag.
Note that the resulting gap may contain unmovable files like special NTFS system files which MyDefrag can not move. Dependant on how you move the temporary file to the beginning, MyDefrag will wrap this file around unmovable files.