Actually the format provider supports the same functionality. The problem is that you cannot create an instance of a TextBlock on the server. The format provider tries to do that when deserializing the document and fails.
If you pre-process the string that you are trying to import and remove the InlineUIContainers, you should be able to use the format providers. If that isn't exactly your issue, you can give us a clue by telling us more about what you want to do with the providers on the server.
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!