it is a natural process as said before.
i got a pair of Black & White Ocellaris Clownfish which would'nt go near my nems, even that they were living in one in my lfs. so i started feeding the nem before them so as to try and intice them,but no!! so i put pair of perculas in as well,took about a week for them to go into me pink tipped, the b+w then took refuge in the same nem, evicted the percs then moved to my bubbletip. the percs are now quite happy using my hippo or torch coral, whateverer takes their fancy, nice to have a second home??? hehe