[Exim] mailman and verp

I'm setting up mailman with exim and found one problematic case. The setup is
exactly as http://www.exim.org/howto/mailman21.html#verpmm says.

Now the problem is that aliases are configured on the same host:

our_aliases:
driver = redirect
domains = domain.pl
allow_defer
allow_fail
data = ${lookup{$local_part}lsearch{/etc/mail/users}}
user = exim

so for example user@??? is redirected to user@???.

Now if I subscribe to some mailman list as user@??? that will be fine
_but_

mailman_verp_smtp:
driver = smtp
# put recipient address into return_path
return_path = ${local_part:$return_path}+$local_part=$domain@${domain:
$return_path}
# must restrict to one recipient at a time
max_rcpt = 1
# Errors-To: may carry old return_path
headers_remove = Errors-To
headers_add = Errors-To: ${local_part:
$return_path}+$local_part=$domain@${domain:$return_path}

will put
Return-path: <my-ml-list-bounces+user=bleble.pl@???>
instead of
Return-path: <my-ml-list-bounces+user=domain.pl@???>
and mailman won't be able to find out for which user the bounces belong.

Any nice solutions to this problem?
--
Arkadiusz Miśkiewicz     CS at FoE, Wroclaw University of Technology
arekm.pld-linux.org, 1024/3DB19BBD, JID: arekm.jabber.org, PLD/Linux