Don't take my word for this, but you might be able to get away with welding. Yes, it is higher heat, but for a much briefer period of time, and in a much more concentrated area. A skilled TIG operator could probably get a boss ina few seconds) and of course, only the area immediately around the boss is heated. You can run a puddle the size of a pinhead with a TIG and still get decent penetration.

Of course, purely theoretical, ask a real framebuilder. A lot of them seem more comfortable with brazing anyway.