Rails - May 2009 - Rails routes with prefix before the :id

This works:
map.connect ''/bananas/pdf/file/:id.pdf'', :controller =>
''bananas'', :action => ''pdf''

This doesn''t work:
map.connect ''/bananas/pdf/file_:id.pdf'', :controller =>
''bananas'', :action => ''pdf''

So once I change the slash to underscore the route doesn''t work the
way I expect it to.
Is there some way I need to escape the routes to make them work (Rails
2.1.2)?