The Editor Utility Widget could be anywhere, if it is in the main Content folder, the relative path should be started with
/Game/path of the utility widget
and if it is in your plugin folder, the path should be like this
/{PluginName}/path of the editor utility
for example:
/MyPlugin/EditorUI/EUW_MyEditorWidget
I am working on a new plugin that has a feature to do this without any CPP code, will be released soon!