Accessing Profile Fields in a DLL

I am trying to use a custom Profile with Memberships to add a few fields to each user's profile:

    <profile>
      <properties>
        <add name="FullName" type="string" />
        <add name="EmployeeNumber" type="int32" />
      </properties>
    </profile> 
I'm a bit confused about how to access them though.
To get at the default fields of a given user I can do this:
  MembershipUser user = Membership.GetUser("jsmith");
  string email = user.Email;
  DateTime loginDate = user.LastLoginDate;
But I can't figure out the syntax for getting at those custom fields.  Also, does it make any difference that I'm trying to access the data from a ...