You could register an adp tag, <contextbar>, and the location of the template file would be hidden. But how about placing the template in the packages/acs-subsite/www heirarchy so that each subsite can control layout independantly?
Can the template not handle the standard list structure of ad_context_bar? It wont be as neat as using a multirow datasource, but it would mean that there wouldn't be a 5th version of the context_bar proc, and only a few templates, not every tcl page, would need to be updated to take advantage.