Create an Excel Add In Application in C#

I'd like to create an Excel Add In. But I want it to have a special behavior.

Then problem is that the Excel Add In I developed stays within Excel. Even when I run a normal Excel instance from Windows...

So what I want, to be more precise, is to have an Excel add in that will only appear in the Excel's ribbon when launched by my own C#_made application.

How should I do that ?

The behavior would be :

Run my C# application
My C# application calls a new Excel's instance
My C# application adds a new tab (and its elements) to the ribbon of this Excel's instance
My C# application adds actions binded to the tab's elements
Excel's instance is being closed > Remove all added components, functions, methods, ...
Close my C# appliclation

Solution

Here's a nice tutorial for you: http://www.add-in-express.com/free-addins/net-excel-addin.php

Edit:

Have you considered just disabling the addin, then reenabling it whenever you launch the app with a server that runs in the background and when excel is closed, disables the addin?

Here's some unload code I found here:

private void UnloadBadAddins(bool unloadAddin)
{
    const string badAddin = "iManage Excel2000 integration (Ver 1.3)";

    foreach(Office.COMAddIn addin in this.ExcelApp.COMAddIns)
    {
        if (addin.Description.ToUpper().Contains(badAddin.ToUpper()))
        {
            if (addin.Connect == unloadAddin)
            {
                addin.Connect = !unloadAddin;
                return;
            }
        }
    }
}