Ok. After many good-intentions and promises, I have finally released the LdapUserManager I wrote last year. The current release has been tested with Orion 1.4.5 and the 1.5.x series. Please feel free to download the source code and/or the binary at http://www.linjafoo.com/projects/ldapum/.
If you have any questions, please feel free to e-mail me. Enjoy! -matthew