How To Handle Covariance Limitations?

This is basically a design problem.

My class structure is as follows:

Interface IA
interface IB<T> where T : IA
abstract class AC<T> : IB<T>

class D : IA
class E : IA
class F : AC<D>
class G : AC<E>

Now, I have a method in AC whose signature is:

void foo(IB<IA> param)

And I want to call it from F like this:

foo(new G())

I know about the limitation of covariance and contravariance, and I know the language doesn't allow it. Also, I can't set IB<out T>.

My question is, what is the correct way to handle such a situation design-wise?