I just pretty much let them get used to one another.
I tried this with Peaseblossom, who was my tailbiter extraordinaire ... and it didn't work for him. He kept biting his tail. At first I kept him isolated, then placed another tank and betta beside him. At first, Boaz, the other betta, wasn't a biter. But I think keeping Peasey and Boaz from seeing one another made the biting worse because Peasey knew that Boaz was there and it caused him stress. Meanwhile, Boaz started biting his tail. And it kept getting worse. I couldn't card their tanks, because they would stress out and bite their tails. And if I didn't card them they would continuously flare.
What I'm doing now is placing tanks together in twos so that they get used to another betta. So far it's working! They also have numerous plants to hide in and I've caught them resting on the leaves. And as long as they have some sort of hide to run away to, it seems okay.
It's really difficult to cure tailbiting because a number of things can trigger it: stress, types of food, no stimulation .... Try a bunch of things. It could be just as simple as the lighting in the room. It's tough to figure it out. But once you get it and correct whatever is bothering them, they might stop. Tailbiting can also be genetic, and in that case there isn't much you can do.
Hope this helps some :)
Also, how does a bottle cap work?
And WOW what a beautiful boy you have! He's so colourful!