I don't think it's possible for online travel agents to book these luxury offers. As far as I have seen all the luxury travel agents need you to call or email them to book these packages.
It's worth looking at that option. I can't recommend any as I use my points when staying at the luxury brands, I know Raffles recommends one on his Head for Points site and others may have their own preferences. They can normally match the best flexible rate but come with extras like double points, $100 credit to use on hotel amenities, breakfast (useful if you don't have status) and an upgrade.