To specify that you want to load the actions in a DLL in the intent session, set the ActionDLLPaths rule. This rule defines the location from which to load DLLs. If you create an "Autodesk ETO Series Custom Host Design Library" project in ETO Series Studio, a UIToolsSettings design generates: 
If you do not use the project template, you can create this design manually, or you can add the ActionDLLPaths rule to the root design manually.