Five months ago, I wrote a piece named Want Your Google News To Show Up in Google Finance? NASDAQ:GOOG which basically said, put the stock ticker in the title of your article and you're golden for showing up in Google Finance. That is, assuming you are already in Google News.
Well, we now have a new tip from Google themselves on how to optimize your content for Google Finance. Inbal from the Google News team said to markup your HTML or XML with the following tags.
<news:title>Companies A, B In Merger Talks</news:title>
<news:keywords>business, mergers, acquisitions</news:keywords>
Adding these elements, along with the title change, should dramatically help you show up in Google Finance for that specific company.
Forum discussion at Google News Help.
Update: Inbal posted an updated version of the sitemap code you also included in your article and if possible she'd like to let the world know about the update. Her last post from here contains the updated code.