You can override the sitemap view mode of the '/content/view/' view. If using ezwebin or ezflow, here is the template you can override and modify : extension/ezwebin/design/ezwebin/templates/node/view/sitemap.tpl.
You will see various call to the following template fetch function :
This is where INI files + ezurl() operator are a good solution. For example, if you want to link to different root nodes per siteaccess, you use something like: