I don't know that you can buy a pass to Loft 19, but you could ask at the check-in desk. Rack rate for the Loft 19 cabanas were $2,000 per week, plus 18% back in May. If you want to rent a cabana by the day, it was $500 plus tip. But on our week, the cabanas were sold out the entire week.
They offered them to some cruisers not in a qualifying suite about 2 weeks before our May cruise at $1,500 plus and we took it. Still pricy but in our opinion, worth it as we are not early to rise people and enjoyed having a space reserved just for us.