I have created a VB6 program using KeepItCool's posted code.
I call the VB6 program from my NSIS installer.
In my limited testing so far it works great!

Thanks for the great tip, Peter.
I've wanted to do this addin install/uninstall stuff for years, and
now I can :)

If I knew how to put a link to the specific post with the code, I
would.
Here is the header for the post.
Newsgroups: microsoft.public.excel.programming
From: keepITcool
Date: Sat, 16 Oct 2004 04:58:50 -0700
Local: Sat, Oct 16 2004 6:58 am
Subject: remove add-in entry via registry

Cheers,

Brian