There is nothing you can do. He either will or will not go to it. Perculas will even sometimes pick something else to host in. Anything from a hairy mushroom to a powerhead. Just give it some time. I've had my false percs for about 3 months and they haven't hosted any of the cool stuff I've got. The only 2 types of clowns that I've always seen take to a host is tomato and maroon.