I don't believe there is a way without having the core. Could be wrong, but I didn't really see anywhere to edit it when I made my own custom heirlooms.
If there is a way outside of the core, it would probably be in the DBC files, which can be rather annoying/tricky to modify, especially due to aging 'DBC Editing' software.
I think you are correct about the DBC file cause I could not see any difference between the DB entry for the stuff that scaled to 85 and the stuff that scared to 80
Thanks ExO the issue is that once a character levels past level 80 they can no longer equip the gear and if NPC Bots are out it removes the gear and puts it in mail and bugs the character