You couldn't add an option to disable it, unless you also added something to display who has it enabled/disabled so the healer knows who they can use it on beforehand. And if there were some people who it couldn't be used on it probably wouldn't be worth having at all since it's such a limited thing.

I would rather have something like a divine benison where I could just bubble someone to be able to take the hit, but I guess that would just become a boring raid tool for use on tanks only.

I like the idea of rescue, but the limited number of situations it's actually useful and my latency make it not a great ability.