migration assistant and transfering mail folders

How can i in mail on 10.5 get it to properly recognise and bless a manually transferred 10.5 mail folder from a backup i made, without using a full-on user migration, as the setup on my old machine is at least 5 years old and has a lot of cruft, and possible slow down issues i dont want to bring to my new system, obviously i can import the mail if i want to but what i really want is to transfer my whole old mail folder lock stock and barrel in functioning form to the new machine without using migration assistant to transfer the whole user.

Once i force may way through first setup and after having placed “mail” and “mail downloads” into the user library mail still treats them like they were intruders, and brings the mails themselves : into a “on my mac” section when i really i wish it was little bit dumber and just recognised and blessed my old mail folder accounts rules signatures the lot. any ideas i was thinking of creating a fake partition with just those bit and getting Migration assistant to just move that mail folder from this fresh and fake user folder but it seems a bit over the top considering there must be a way to get mail to bless and use a users mail folder ?