Create an aliasing between an LDAP user and its MySQL user equivalent. This will take a new table to establish the relationship between the current mysql user and its ldap account (can you get the sid from an ldap, or maybe just stuck with dn). Then write an adapter to stand between the mysql account and the ldap account which is capable of resolving a ldap name as a mysql id. This can now be used to associate anything owned by the mysql user with the ldap user.
If you're OO, its likely that this will only take a few minutes. If you're procedural, I'd expect it to take a lot longer.