Assign "Get External Data" from a VSTO Add In

Hello,

I would like to be able to assign a web service as external data for a
Worksheet. I need this to be done through a VSTO add in for the Ribbon in
Excel 2007.
The code might look like:

public void XMLAttachment()
{

this.Sheet.GetExternalData.WebServiceURL("https://someService.asmx/getData?startMonth=200708");
}

I want the Excel sheet to load the XML exactly as it does when this is done
through the User Interface.

Thanks in Advance,
John M.