@Tim As a suggestions, perhaps setup the mailing list to put something like a header saying "Please post replies below the footer to keep things organized" and a footer saying "Please reply below here to keep things organized" on every message coming through the mailing list? It's what we do with the Ark Linux mailing list (at least with the footer). Perhaps make it bold so people won't miss it (of course, some people disable HTML in their email clients, so the bold may just get in the way).
Good idea--I am attempting to get this implemented ASAP.
Tim