There are ways of traversing the siteMap nodes to get the topmost parent and then the parent node has the properties for page name url etc.
While I don't have time to code it up for you, you can look in the SiteMenu.ascx.cs for logic how to get the root site map node, and you can look in /Compoenents/SiteUtils.cs to see some methods where I navigate nodes in helper methods. Like you can get the current page node by calling
SiteUtils.mojoSiteMapNode currentNode = GetCurrentPageSiteMapNode(rootNode);
Then get the parent node with
mojoSiteMapNode topParent = SiteUtils.GetTopLevelParentNode(currentNode);
Hope it helps,