Actually if you want to just dress him in Jame's clothes you could probably use James Casual by simply hiding the built in clothes sections via the hierchy editor and thenm conforming any of regular Jame's clothes  to the casual figure. You wouldn't be able to use any clothes with short sleeves or pants though because hiding the casual figure clothes would mean no belly buttons, midrifts or other skin parts would show where the clothes had been hidden. You're definately better off startuig from scratch with nude James and dressing him as you want him. You might be able to save the faceroom data from Casual James as a PMD and loading it to Nude james, but I'm not certain without opening them and trying it myself.

Oh, and casual Jame's clothes show up as actual body parts in the heirchy editor like Chest, Hips, Thigh, shin, forearm etcetra....