Hello @anon50128360,
multihoming tasks in a separate project that you share with the client might be an option. Have you considered that already?
Now to ensure that works well be careful regarding subtasks. For example if you have one task with many subtasks but your client should not see all, then it might be better splitting up things into tasks in general. Bastien has shared a great post about this today: 💡 Subtasks: when to use them, when not to use them
And here is a post, related to how much access to give clients, that you might be interested in: 🚦 Dealing with external clients - How much access should they have?