Microsoft will only use your sitemaps file if it is listed in your robots.txt file. You cannot currently ping Microsoft or upload your sitemaps file to Microsoft.
Microsoft, along with Ask.com, Google and Yahoo, united to support autodiscovery of sitemaps in April. Google, Yahoo and Ask.com quickly supported it on that day or soon after. Microsoft finally began supporting the reading of these sitemaps files as of yesterday.
How do you specify the location of your Sitemaps file in your robots.txt file? Just add a line like this:
Replace the <sitemap_location> with the absolute URL for the file.
More details at Sitemaps.org.