http://www.coactivate.org/projects/deliverance/lists/deliverance-discussion/archive/2011/04/1302098171632

filter.py

### mymodule/filter.py
class PageClassFilter(object):
  def __init__(self, inner_app, classes):
    self.inner_app = inner_app
    self.classes = classes
  def __call__(self, environ, start_response):
    environ['deliverance.page_classes'] = self.classes
    return self.inner_app(environ, start_response)

def filter_factory(*args, classes):
  classes = classes.split()
  def filter(app):
    return PageClassFilter(app, classes)
  return filter

paste.ini

### paste.ini
[composite:main]
use = egg:Paste#urlmap
/foo = app1
/bar = app2

[app:app1]
use = egg:MyProject#app1
filter-with = app1-filter

[app:app2]
use = egg:MyProject#app2
filter-with = app2-filter

[filter:app1-filter]
paste.filter_factory = mymodule.filter:filter_factory
classes = class1 class2

[filter:app2-filter]
paste.filter_factory = mymodule.filter:filter_factory
classes = class3 class4 class5