Create a button in toolbar via setup or run script

I need to create an add-on for lotus notes in form of a button on the toolbar. However one of the requirement is that while installation of the add-on minium end user interaction should be required. i.e. the add-on will be given users in form of a setup or a script to run and users don’t have to manually set anything.

Therefore I am using C APIs to do this. But I have not found a way to create a button in toolbar in C APIs. I want to access the toolbar using C APIs. Can anyone give me some reference for doing this ?