FakeItEasy - How to have an interface fake inherit from abstract?

I have an interface

interface IInterface {}

An abstract class

abstract class AbstractClass : IInterface { }

Concrete class

class Irrelevant { Irrelevant (IInterface service) {} }

I'm writing a unit test against Irrelevant and the abstract class already contains helpful methods I'd want to leverage for my unit test. How would I make my A.Fake<IInterface>(); inherit from AbstractClass?