I have been planning to get a second betta for a few weeks. My current betta, John, does flare when he sees my sister's betta and goldfish. He did not flare around my friend's 3 bettas, however.
If in fact I do get a new betta, my idea is to put the tanks not too close together, but close enough that John could see the other betta. Maybe a foot or so apart, and move the two tanks a little closer, about a centimeter or 2, every day or so.
Could this idea work?