[CONNECT C++] DependencyManagerLinkage::IRootsChangedCallback

I'm uncertain how to use this struct.  It contains two pure virtual methods, so I should do something like this...

struct MyDependencyCallback : Bentley::DgnPlatform::DependencyManagerLinkage::IRootsChangedCallback
{
  virtual StatusInt  OnRootsChanged (ElementHandleCR   dependentElement,
                           Bentley::DgnPlatform::DependencyLinkage const& dependencyData,
                           UInt8*                        pRootStatus,
                           UInt8                         selfStatus) override;
  virtual WString  GetDescription () const override;
};

However, I can't create an instance of that because IRootsChangedCallback inherits from RefCounted, which also has virtual pure functions.

I want to pass MyDependencyCallback::OnRootsChanged to DependencyManagerLinkage::RegisterRootsChangedCallback.  What am I doing wrong?  How should I register my dependency callback?