PRISM handling SubscriptionToken

The PRISM event aggregator is awfull on my point of view. Well, I'm trying to call SubscriptionToken.Dispose without too much code in the every ViewModel, so what I'm trying to do is the following:

public abstract class EventViewModel : NotificationObject, IDisposable
    {
        private Collection<SubscriptionToken> tokens;
        protected IEventAggregator EventAggregator { get; private set; }

        public EventViewModel(IEventAggregator eventAggregator)
        {
            EventAggregator = eventAggregator;
            tokens = new Collection<SubscriptionToken>();
        }

        protected void SubscribeTo<TEvent>(Action<TEvent> action)
            where TEvent : CompositePresentationEvent<TEvent>, new()
        {
            tokens.Add(EventAggregator.GetEvent<TEvent>().Subscribe(action));
        }

        public void Dispose()
        {
            foreach (var token in tokens)
                token.Dispose();
        }
    }

public PreviewInputViewModel(IEventAggregator eventAggregator, INavigationService nagivationService,
            IMixerOrchestrator orchestrator, Input input)
            : base(eventAggregator)
        {
            this.nagivationService = nagivationService;
            this.orchestrator = orchestrator;

            SubscribeTo<EditInputConfirmedEvent>(EditInputConfirmed);
            SubscribeTo<EditInputCanceledEvent>(EditInputCanceled);
            SubscribeTo<MixerStartedEvent>(MixerStarted);
        }

private void EditInputConfirmed(Input input)
        {
            
        }

private void EditInputCanceled(Input input)
        {
        }

private void MixerStarted(Uri source)
        {
           
        }

However, I can't do that because the Action<TEvent> that I have to implement is Action<EditInputConfirmedEvent> and not the "payload" of that class (Action<Input>):

public class EditInputConfirmedEvent : CompositePresentationEvent<Input>
    {
    }

Take a look at WPF FlashMessage
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