Custom CreateUser Method With Additional Parameters - Store In The Db

i have implemented custom MembershipProvider and now i would like to use CreateUserWizard to create new users.. the problem is that i want to store in the db more information that normally (e.g. first and last name). There is function:

public override MembershipUser CreateUser(string username, string password, string email,
string passwordQuestion, string passwordAnswer, bool isApproved, object providerUserKey,
out MembershipCreateStatus status)
{
throw new NotImplementedException();
}

which i can implement but it won't store first name etc. i found here: [URL] solution that i can overload this function and call it manually but the default CreateUser function will still be called in this case...