Wouldn't have to be clamped at the top where it enters the raceway, only where it enters the box. You don't strip the jacket off the NM inside the raceway, only as usual at the box so ther is no need to use a connector where it enters the Wiremold. The Wiremold only sleeves the NM. You can do the same thing with EMT instead of Wiremold if the appearance is not an issue.
-Hal
