Is your clownfish hosting in anything right now? If so, removing it (the non-anemone host) may speed up the process.
What's worked for me on 2 occasions was keeping them in a small area together. I acclimated my GBTA and percs together and they hopped in. Another time, i kept the bta and clown in a little quarantine bin together in the main DT and after a while he hosted.
Try keeping them in a small, but not too tiny, area together. One of those critter keepers from a petsmart worked for me.
I am not a fan of "forcing" clown to host by putting them in a confined space with an anemone -- sure it might work, but if the clowns aren't ready they very well could end up eaten.
I was told to tape pics of clowns in nems onto the tank and they will learn that they are supposed to go into them.... well I put the pic up on the side of the tank and within 3-4 days they were checking out the nem.... not sure if it worked or they were finally curious..
I've always found this hilarious. Not that I think it doesn't work, but that the concept is just funny to me. I might have to try that same tactic for spawning LOL!
What has worked for me is to find a friend who breeds clarkii and add a little tiny one to the tank. Clarkiis go into anything. So, when your clowns see another clown hosted in the nem that is smaller they will kick him out and claim it for themselves. Jealous little buggers.
Then the clarkii either becomes a sump fish or else goes to the LFS for store credit.
I don't think this is really true.So Clarkiis are wild bred or captive bred? cuz usually captive bred, they do not know what an anemone is lol