I have see it before couple time in Wisconsin and really it was a hard item to back up due the NEC did not excatally describe as you say in first place and I did review the NEC { 2005 and 2008 NEC verison } and I just can not excatally nail it however jump over to Electrique Codé France { Basically a French verison of NEC but used in France } and came up a sweet spot where I found and it say with T&E { twin and earth the same as your NM cable } with extra conductor in raceway is not allowed the only time it will allowed if all indivual conductors.

Merci.
Marc

Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)