Addition of User Properties

Hello everyone... I am currently involved in a project that requires that we create and store proprietary user properties. The break-down goes like this:

Primary user information is coming from a read-only LDAP (the official SAP corporate LDAP to be precise). Since we cannot store any user-specific attributes there, we need a way to store them somewhere else in a way that when a user logs on, these extraneous attributes are available from the same user object that you get the user's firstname and lastname from.

What's more, we need to persist these attributes, allowing users to occasionally change them (hopefully) through their user profile page. How to add fields to the user profile page, then have those values propagate to a specific user attribute store is another big question that I cannot find an answer to in the existing documentation.

I've had suggestions to use another LDAP server, like eDirectory, to store these new user attributes, but I cannot find any way to attach another LDAP in a way that allows it to add it's attributes to those coming from the main user store in the common user object accessible from within a component's code.

Anyone have any ideas?