have you looked in the user track bar setting options
intros, they should be doing them soon as the boss said he was adding lots of new features to user tracks and ones that have been requested for years http://www.pgmusic.com/forums/ubbthreads.php?ubb=showflat&Number=331413#Post331413
not sure about C,D you could just try it with one, just put another instrument at those part markers - save the user track then try it with those part markers in place and see if you get the other instrument come in on them.

Hope that helps - lets us know if they work