You could still have the client use Apple as a proxy. This would reduce the privacy of the message but only the URL and only exposing it to specific service at Apple. If it is a SOCKS proxy, you could reduce the exposure to just the IP address and some amount of leakage to whatever DNS server the phone is using.

The client can still ask the Apple server for the metadata, since Apple already knows your IP from the push notification channel anyway. Ideally Apple would ensure that this lookup is not logged or stored in any way so there's no repository of the links people have sent to you anywhere.

The client could send the request to Apple though, and pass the URL through that way, instead of requesting the actual URL. There's a trade-off there though that Apple gets to see all the links being sent over iMessage.