How to allow Undo on project assets created with an editor script?

I've developed an editor script for organizing my project assets. It takes a selected prefab in the project panel, creates a folder structure then moved the prefab into that structure. Most of this is achieved using the AssetDatabase library.

I want to include the ability to undo this operation, but am having trouble finding an undo operation that works in the project panel. It seems that Undo.RegisterUndo() and Undo.RegisterSceneUndo() both only work on hierarchy changes.

How can I get undos working when I make programmatic changes to the project assets?