This is a method that has also been used on quite a few frames and there are some notable frame builders who have also used filler to correct less then perfect brazing work or to get a more aerodynamic shape that would be impractical with brass.

By using filler you will not have to worry about affecting the existing joints or cooking the tubing... in some cases you may have to use a good amount of what is expensive brass which would involve longer heating cycles while filler can be done cold.