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.
Code:
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.