Yeah you will probally need to recode the whole thing how it works. Thats really a mysql limitation and since we store it in the mysql date field there is not much I can do to change that.
The birthday is only displayed one place in the profile when viewing the profile. Maybe altering member.php to add this in bold.
Content visible to verified customers only.
You can then edit the profile template and change $birthday to $birth2
Aside from that you can ask further code modification questions in THE MOD CORNER outside product support.