Laravel Notifications - Queue ONLY on toMail method?

I've set up Laravel Notifications and so far so good. My set up is that i'm sending two notifications: "mail" and "database". I plan on having the database notification so that I can display the notification somewhere and allow the user to clear it.

The problem is, when I queue the entire Noitification class, as expected, everything is queued... so this means that even database notifications are queued as well. I would like only the "mail" portion to be queued while the database portion is instantly stored to the database. Is this possible?

Here is the class so far.

<?php

namespace App\Notifications;

use Illuminate\Bus\Queueable;
use Illuminate\Notifications\Notification;
use Illuminate\Contracts\Queue\ShouldQueue;
use Illuminate\Notifications\Messages\MailMessage;
use App\Document;

class ViewedDocument extends Notification implements ShouldQueue
{
    use Queueable;

    protected $document;


    /**
     * Create a new notification instance.
     *
     * @return void
     */
    public function __construct(Document $document)
    {
        $this->document = $document;
    }

    /**
     * Get the notification's delivery channels.
     *
     * @param  mixed  $notifiable
     * @return array
     */
    public function via($notifiable)
    {
        return ['mail','database'];
    }

    /**
     * Get the mail representation of the notification.
     *
     * @param  mixed  $notifiable
     * @return \Illuminate\Notifications\Messages\MailMessage
     */
    public function toMail($notifiable)
    {
        return (new MailMessage)
                    ->line('The introduction to the notification.')
                    ->action('Notification Action', url('/'))
                    ->line('Thank you for using our application!');
    }

    /**
     * Get the array representation of the notification.
     *
     * @param  mixed  $notifiable
     * @return array
     */
    public function toArray($notifiable)
    {
        return [
            'document_id' => $this->document->id,
            'document_title' => $this->document->title
        ];
    }
}

... And im calling it in a controller somewhere ...

// notification
Notification::send(User::find($document->created_by['user_id']), new ViewedDocument($document));

Thanks