Unfortunately, no. Even if you somehow patched that part of ItemMeta, you'd still run the risk of losing data if the server is run without your plugin. Not to mention that such a patch would probably run afoul of the BukkitDev policy. Your best bet is to store the data (or a reference to the data) as a part of standard ItemStack data, such as lore, name or attributes. I prefer attributes as its (mostly) invisible to the user, but you could also store the data in the lore section and use ProtocolLib to hide it. Just read this thread for more information.