Issue with slash symbol in @route declaration

I have an issue with dynamic @route declaration:

@handler('test')
def MainMenu():
    oc = ObjectContainer()
    group = Prefs['group'] # for example aaa/bbb
    oc.add(DirectoryObject(key = Callback(ListItems, group = unicode(group)), title = group))
    return oc

@route('test/listitems/{group}', page = int)
def ListItems(group, page = 1):
    items = Dict[group]
    for item in items:
        ....

I get an error stating that url test/listitems/aaa/bbb is not found, how can I escape it to something like test/listitems/aaa&#47bbb or similar? aaa/bbb value is being red from preferences, provided by user.