The top, right panel and bottom will all have to be changed I think.
Just took another quick look, yep, he has parts of images on other images, much easier to mod when top, places, programs, more prog backgorund and bottom are their own images. If those bits of more progs back and progams sides where not on bottom panel it would just easily stretch to make full start menu, it still may stretch but painting margins will need adjusting.
JJ does great work but I am not sure why he made the images the way he has.