How can I mock Elmah's ErrorSignal routine?

We're using ELMAH for handling errors in our ASP.Net MVC c# application and in our caught exceptions, we're doing something like this:

ErrorSignal.FromCurrentContext().Raise(exception);

but when I try to unit test the caught exceptions, I get this message:

System.ArgumentNullException: Value cannot be null.
Parameter name: context

How can I mock the FromCurrentContext() call? Is there something else I should be doing instead?

FYI... We're currently using Moq and RhinoMocks.

Thanks!