While you cannot exclude products from the Sitemap file, you can override the head-tags variable for specific pages they do not wish search engines to index and insert the following:

<meta name="robots" content="noindex,follow">

This asks the search engine robot to not index the page but to follow any links on the page to other pages which you may or may not want indexed.

Note: This is not recommended as you may have products excluded from search engines indexes for longer than you wish. It is recommended that you allow the page to be indexed by setting the product to not orderable (or not available if using real-time or database inventory features).