Custom MembershipProvider SharePoint FBA and the user's display name

Question

we are using both windows authentication and forms based authentication in a claims aware SharePoint WebApplication. The custom MembershipProvider (datasource: Novell eDirectory) works just fine but I'm uncertain about a few things.

The cn property of each user record is a unique identifier (hexadecimal value). Users are logging in using their email addresses (and password) though. We don't want to make the unique identifier visible anywhere.

GetUser(string username, bool userIsOnline)
FindUsersByEmail(...) and
FindUsersByName(...)

return MembershipUser(s) which are constructed this way:

CustomMembershipUser membershipUser = new CustomMembershipUser(
            providerName: Name, // the membership provider's name
            userName: providerUserKey, *// the "cn" name*
            providerUserKey: providerUserKey, *// again the "cn" name*
            email: email, // the email used to log in
            passwordQuestion: null,
            comment: null,
            isApproved: true,
            isLockedOut: false,
            creationDate: DateTime.MinValue,
            lastLoginDate: DateTime.MinValue,
            lastActivityDate: DateTime.MinValue,
            lastPasswordChangedDate: DateTime.MinValue,
            lastLockedOutDate: DateTime.MinValue,
            firstName: givenName,
            lastName: surName);

The last two parameters are "Custom-"MembershipUser parameters. My ultimate goal is to display users in an Windows-Integrated-Authentication-style "LastName, FirstName".

Right now upon entering my email address the people picker resolves my email address to a "cn" name which is something like XYZ12345. Instead I want to display "LastName, FirstName" throughout SharePoint. The information is present in the datasource (eDirectory) and I can enrich my CustomMembershipUser with this information but of course neither the PeoplePicker nor anything else in SharePoint will be aware of my custom MembershipUser.

Is there anything claims related I should be aware of?