Everybody loves Anonymous Delegates

public override int AddResource(T resource, string externalKey)
{
    int internalKey = base.AddResource(resource, externalKey);

    // When a resource is added it's reference is auto set one

    resource.ReferencesAreZero += delegate(object sender, EventArgs eventArgs)
    {
        RemoveResource(internalKey);
    };

    return internalKey;
}