Does anyone know how incorporate a custom wrist holder icon in a Half-Life: Alyx addon map?

I want to be able to place a custom model in the wrist item holder. I made a model and checked "Allow in Item Holder" under the prop_physics object parameters. My model can be placed into and retrieved from the wrist holder.

However, item holder objects also have a transparent "icon" that is shown in the holder so you can see what item it contains. When I place my model in the wrist holder, it displays the icon for the health pen. I assume this model is a default. So I need to override this somehow.

The wrist holder icons seem to be separate models, as they exist in the Alyx model assets. So I made a transparent version of my model but can't figure out how to incorporate it. There doesn't seem to be a node in the ModelDoc Editor for referencing the icon model, or a model Archetype for it. Can anyone help me with this?