Well, you can try injecting them but it's never worked for me. They always grow back

I've got a copperband butterfly in the tank right now in hopes that the fish will eat them but it hasn't even pecked yet. I'm assuming that once it's eaten all of the fan worms, it'll pay more attention to the anemones.
As for where to get syringes, I got mine at my local pharmacy but not everyone can just ask and receive needles this easily. I think I got lucky
Personally, instead of boiling water, I'd try to inject them with kalk paste. Because you won't be able to get a paste that thick through a needle, you'll need a larger syringe (like the plastic ones that come with the Salifert test kits that you use to measure your test water with). What I do is mix enough kalkwasser and r.o. water to make a thick paste and try my best to drop a glob of it directly on the amemone's mouth. I've read somewhere that if you "flavor" the paste with a bit of fish food, the anemone might grab the end of the syringe as a feeding response and it would be easier to inject the glob of kalk directly into its mouth. I have yet to try this myself.