Turns out it is possible. I’m not sure if it was previously there in Unity 4.3 but I just found out about the order property that’s in PropertyAttribute. So now you can composite/decorate attributes like:
[Comment("This is a comment"), order = 0]
[ShowTransform, order = 1]
public Transform t;
Just make sure the order makes sense.
Also worth mentioning that Unity changed the way they deal with properties internally. They now have a PropertyHandler from which PropertyDrawer and PropertyDecorator inherit from. I’m happy Unity did something right and implemented composition.