How to add via lotusscript or API a toolbaricon to designer toolbar

I created a .NET application (Lotusscript Manager, look @ openntf.org) and I would like to add it via a script button to a new or existing toolbar as a smarticon in the Lotus Designer client.

I found code in the Teamstudio’s Scriptbrowser to install a smarticon but they are using some sort of dll I can’t find.

Also on openntf there exists a project “Notes Design Searcher” where a smart icon will be installed, but that sollution is not that great.

Tried exporting the DXL of a manual created smart icon but the smart icon formula won’t be exported.

Does somebody have a better idea?