We have addressed simialr request in the support ticket you have submitted on the issue, you can find our response there. For your convenience I'm pasting ti below as well:
1. In the user list, users from our custom provider show up with email/name column as "User not found". Is there a reasonable way that we can get profile information from our existing data? The forums seemed to indicate that a custom Profile Provider is not possible yet, so what is the suggested way to update and sync profiles between Sitefinity and another system? (users are imported into that other system from other sources, so it would be a fair amount of work to redo the import process)
As you properly pointed out, the DisplayName parameter from the users List control is taken from the userprofile (it's a concatenation of the user's FirstName and LastName profile fields). The rest (Username, Email, CreationDate, and LastLoginDate) are pulled directly from the user's properties. A possible reason for the UserNotFound exception is that the provider is nto returnign a user with this ID, or the Email/UserName properties of the User object you're returning to Sitefinity are not set.
Regarding the UserProfile data, you can rely on the out of the box Profile provider implementation - once you edit your users that are pulled through custom MembershipProvider, Sitefinity will create profile entries for these users.
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