How do you add extra sub-assets into an asset while importing?

Hi,

I'm trying to write an asset post-processor that runs each time a model is imported. I want it to add new sub-assets into the asset, just like the Mesh, Material and AnimationClips that you get by default when you import something. In this particular case, I want to add an extra AnimationClip in that I've made procedurally.

Unfortunately, while I can hook into the process easily enough, trying to actually add the asset seems impossible. Here's the best I could come up with. It runs without error, but my new clip doesn't show up. The asset imports as usual but nothing's changed.

I also tried using AssetDatabase.AddObjectToAsset instead, but it seems that's not intended to be using during import, instead to be called after an asset's been made?

 public class MySuperModelProcessor : AssetPostprocessor
 {
     void OnPostprocessModel(GameObject g)
     {
         if (assetPath == "Assets/test.blend") {
             Debug.Log("Adding new objects into asset: " + assetPath);
 
             // Attempt to add an extra clip in there:            
             AnimationClip clip = new AnimationClip();
             clip.name = "My New Clip";
             
             context.AddObjectToAsset("my_new_clip_id", clip);
             // ^^^^ This call seems like it should do the job,
             //      but instead returns without error and does nothing.
         }
     }
 }