Very simple. I have an autoping script I coded a while back, basically you just enter your sitemap/rss url and hit "PING" and off it goes. Very simple method, all you need to do is execute a GET request to http : / / www.go_o_gle.com/webmasters/sitemaps/ping?sitemap={sitemap_url}
obviously, remove the spaces and underscores, and replace {sitemap_url} with your sitemap/rss url.