Add a new SolutionItem to a Solution

Hi,
is there a way to add a new SolutionItem into an existing Solution?
SolutionItem will be an .xml file (think of it like a config file) so is not a new project!

I found this:

http://www.dotnet247.com/247reference/msgs/10/53303.aspx

But seems a little old, maybe there's something more correct using VSeXtensibility or EnvDte.
File added is general for all the projects in a Solution and need to be under Visual Source Safe.

I am using C#, VsPackage and Visual Studio 2008.

Thanks for any suggestions.

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- Matteo Garzulino -