Many to Many Hybrid relationship

[lucabartoli]

My code (not relevant parts omitted):

class User extends Authenticatable
{
    use Notifiable;
    use HybridRelations;
    protected $connection = 'mysql';

    public function messages()
    {
        return $this->belongsToMany(Message::class);
    }
}

use Jenssegers\Mongodb\Eloquent\Model as Eloquent;
use App\Models\User;

class Message extends Eloquent
{
    protected $connection = 'mongodb';
    protected $collection = 'messages';

    public function users()
    {
        return $this->belongsToMany(User::class);
    }
}

Now:

Message::first()->users()->attach( User::first() ); //Stores in the pivot table in MySQL
User::first()->messages()->attach( Message::first() ); //Stores in the embedded relation in MongoDB

The issue now is that I'm only able to retrieve the users from a message (if I used the first method) OR viceversa.

Is it possible to specify the connection on which the relation is stored?
So I would be able to update and read both object from both the relations.