This is not the way. Remember, most if not all instances are non for profit. If you force an instance to host all of the federated lemmy content even content nobody on that instance is subscribed to it will have a financial cost that I think no admin is willing to pay. Also admins will soon be purging data that is not being subscribed to by the users of that instance, so it will just be a waste of time, and might even get you banned from that instance.
ah sorry my bad, misunderstood your post. I agree then, sounds like a useful feature.
Be sure to check out the github issues for jerboa there might already be someone asking for this.
If not, you should think about creating one. It will have a better chance of devs responding than here.