Maybe there is some clever way of doing this with the @In feature that I am not aware of. Until someone enlightens you and me I think you should be fine with:

AbstactContentMessages contentMessages = 
  (AbstactContentMessages) Component.getInstance("nameOfSubComp");

I hope it helps.

/Tobias

If you use

@In
AbstractContentMessages contentMessages;

Combined with (can be in a different POJO or EJB class)

@Factory("contentMessages")
public AbstractContentMessages create() {
   // return different subclasses here.
}

Would that work? I've been using @Factory extensively to enable the use of a polymorphic EL expression. You can also try out the more obscure @Unwrap annotation, even though I never used it myself. The main difference between the 2 is @Unwrap is called everytime it is referenced. @Factory is only called if the corresponding EL expression can't be resolved in any contexts.