Of course, even as I say that my brain is scheming for a way to give them a tool that could auto generate data entry for all of our interfaces and allow them to bypass the UI... I can't help it, it's the twisted mad scientist in my head!
Use
SpecFlow with bindings that talk to the REST API. You write the bindings; they write the BDD tests (using Gherkin syntax). SpecFlow generates NUnit (or MbUnit, or...) unit tests that you run on your CI server. You can also use SpecFlow with MSTest and the Silverlight Unit Testing framework to automatically test via the UI.