I don't know how to pass Object Attributes but if it is referring to the object name, that should work. Select by filter the body or curve or... (not the parametric feature), then go to properties (or go to edit properties 1st) , the the General tab and name the object. see if that works.
Are "attributes" (by whatever name) even supported by the STEP specification?
Production: NX10.0.3.5 MP16/TC11.2
I'd rather be e-steamed than e-diseaseled