Apparently duplicate URLs are allowed in the urlconf, and the first match listed will have priority:
urlpatterns = patterns('',
(r'^$', include('glue.urls')),
(r'^foo/', include('foo.urls')),
# This will override the same URL in bar's urlconf:
(r'^bar/stuff/$', 'glue.views.new_bar_stuff', {'arg': 'yarrgh'}, 'bar_stuff'),
(r'^bar/', include('bar.urls')),
)