The target would be his UTC file, since that's where his inventory is stored. As to how you'd do it, while you could just edit the UTC directly and add it to his inventory via Holocron Toolset or KGFF, a better approach might be to use scripting to do it, since that allows for more control. It would also mean it wouldn't be affected by the edge case of people loading a save where he had already been spawned before they installed the mod, since in that case a modified UTC wouldn't take affect (creatures, placeables, etc. are saved in the GIT file stored in the user's save as soon as they are spawned). Probably not a big deal in this instance, but it can be a significant consideration in other circumstances.