How to add a new Class in a Scala Compiler Plugin?

In a Scala Compiler Plugin, I'm trying to create a new class that implement a pre-existing trait. So far my code looks like this:

def trait2Impl(original: ClassDef, newName: String): ClassDef = {
    val impl = original.impl
    // Seems OK to have same self, but does not make sense to me ...
    val self = impl.self
    // TODO: implement methods ...
    val body = impl.body
    // We implement original
    val parents = original :: impl.parents
    val newImpl = treeCopy.Template(impl, parents, self, body)
    val name = newTypeName(newName)
    // We are a syntheic class, not a user-defined trait
    val mods = (original.mods | SYNTHETIC) &~ TRAIT
    val tp = original.tparams
    val result = treeCopy.ClassDef(original, mods, name, tp, newImpl)
    // Same Package?
    val owner = original.symbol.owner
    // New symbol. What's a Position good for?
    val symbol = new TypeSymbol(owner, NoPosition, name)
    result.setSymbol(symbol)
    symbol.setFlag(SYNTHETIC)
    symbol.setFlag(ABSTRACT)
    symbol.resetFlag(INTERFACE)
    symbol.resetFlag(TRAIT)
    owner.info.decls.enter(symbol)
    result
}

But it doesn't seem to get added to the package. I suspect that is because actually the package got "traversed" before the trait that causes the generation, and/or because the "override def transform(tree: Tree): Tree" method of the TypingTransformer can only return one Tree, for every Tree that it receives, so it cannot actually produce a new Tree, but only modify one.

So, how do you add a new Class to an existing package? Maybe it would work if I transformed the package when "transform(Tree)" gets it, but I that point I don't know the content of the package yet, so I cannot generate the new Class this early (or could I?). Or maybe it's related to the "Position" parameter of the Symbol?

So far I found several examples where Trees are modified, but none where a completely new Class is created in a Compile