C# auto-add all namespaces found in XmlNamespaceManager

I have the following tiny C# console app which reads an XML and searches a value of a tag using a single XPATH. i don't want to change the way it is implemented (via navigator) but I need a small function to add the namespaces; otherwise i can't use it in many different XML documents. May you help me?
Below what I have (working):

using System;
using System.Xml;
using System.Xml.XPath;

namespace ConsoleApp1
{
    class Program
    {

        static void Main(string[] args)
        {
            XPathNavigator nav;
            XPathDocument docNav;
            XmlNamespaceManager nsMgr;

            // Openning MYXML doc
            docNav = new XPathDocument(@"c:\Users\Somebody\Desktop\xml\MYLASTXML.123456.MYXML.xml");

            // Creating a navigator to query using XPath.
            nav = docNav.CreateNavigator();

            //Add Namespaces for scb and conf
            nsMgr = new XmlNamespaceManager(nav.NameTable);
            nsMgr.AddNamespace("abc", "http://www.ababab.com/MYXML-1");
            nsMgr.AddNamespace("conf", "http://www.fpml.org/FpML-5/confirmation");
.... //I should continue add namespaces here but I need a function to populate with all namespaces found in the XML document..... can you help?

            nav = docNav.CreateNavigator().SelectSingleNode("/abc:MYXML/blahblahblah/conf:productId[@productIdScheme='http://www.fpml.org/coding-scheme/external/instrument-id']/text()", nsMgr);

            Console.WriteLine(nav);
            Console.ReadLine();
        }
    }
}