I've done BB before. So, I am an advocate if that's what you like, but if you really want a carpet that badly why not just slowly add some sand in? There are bound to be areas of your tank that have lower flow. You can mix grades of sand to keep it in place. If you add rubbel rock and crushed coral to the high flow areas you should be able to add aragonite to the lower flow areas. The anemone will seek out what it likes. You just want to use your best guess on where you think it will be happy and focus less on where you would like to see it. Pick a spot with the most sand and light. That is likely to be a lower flow area anyway just because sand won't collect as much in the high flow areas.
I've only kept two haddonis. One was a loooong time ago. I think that one melted. The other was a rescue in my BB 210 gallon. That one attached and grew really well in a spot that collected detritus, dead sps frags and liverock sheddings until I did something to make it mad (I think i dropped a coral on it) and it wandered off into a closed loop. That system had about 11,000 GPH on it during high flow periods and about 6,500 GPH during low flow periods and 1000W of 14KK MH lighting. I had two Reeflo Barracudas on CLs (one which cycled on and off about every 6 hours) and a 2,000GPH (Little Giant?) return.
That's about all I have to offer.... Todd is a good guy to speak with about the specifics of haddonis. He's successfully kept several of them for years at a time.