dunno if this feature is new since you posted - when i created my discussion list, one of the options was to "Create Convenience Addresses". if you select this, you'll get mail aliases created against the primary domain that bounce over to the lists. subdomain.
so my list "bob", which is technically connected to lists.suckefree.com will work if i mail to email@example.com, with all the administrative email addresses working as well ( like firstname.lastname@example.org)
at least, that's how it's supposed to work. right now, i'm getting an error on my lists that all the admin addresses are missing from the virtual user table