CiviCRM Community Forums (archive)

Currently it is hard-coded, and this has been a long-standing itch that no one has yet scratched. Until someone (maybe you!) converts it to a profile, I don't recommend using the honoree section at all; with only first_name, last_name and prefix exposed, you get some pretty weird contacts entered into the database like "Mrs. My Mother"
Current workaround is to use custom fields or (my preference) the contribution note field, which allows people to write whatever they want and your staff can sort it out into CRM data much better than the general public would ever do no matter what fields were exposed.
Alternately if you are on D7 you can use Webform-CiviCRM v4 which has a much more flexible approach to contact ref fields and would allow you to customize honoree however you want.