Maybe after the dust has settled it would be worth investigating to install a local NNTP server (INN) and the mailman-to-usenet gateway? Or some way to give an NNTP server access to the mailman archive? (I don't know how the archive is stored in mailman... is it just a collection of mail files, 1 message per file?)
Of course it would require some study and maybe some hacks, it would e.g. be nice when the NNTP server authenticates the users using the mailman accounts (until we have that general authentication service, at least...)
Rob