[Exim] exim3: putting spamassassin in front of uux

my uux transport looks like

    uux:
      driver = pipe
      command = "/usr/bin/uux - -r $host!rmail ($local_part@$domain)"
      path = "/usr/local/bin:/usr/bin:/bin"
      return_fail_output = true
      user = uucp

being driven by the following router

    force_uucp:
      driver = domainlist
      route_file = /usr/local/etc/exim/ro.uucp
      search_type = partial-lsearch

against a file which looks like

    # Domain       Relay  Transport
    # ------       -----  ---------
    foo            foo    uubatch
    *.foo.co.uk    bar    uux
    foo.co.uk      bar    uux

and i want to put spamassassin in front of some of the relays.

is there a common hack, especially one which moves easily to v4?

randy