I don't know if I'd purposefully herd your clowns toward the anemone. If they're not sufficiently protected against the sting of the anemone, they can die. I'd just give them time, especially if they are still quite young. Some clownfish in the ocellaris/percula families won't ever use a bubble tip as their host, as it's not their natural host. Others will warm up after some time. My pair of ocellaris clowns ignored my RBTA for about a month before they finally swam in over a stretch of a few days. I'd just be patient.