If I concatenate multiple visualisations, is it possible to change the spacing between them easily?

For example:

"spacing": 0,
"hconcat": [
  {..}, <- chart 1
  {..}, <- chart 2
  {..}, <- chart 3
]

Is there a way to make spacing between chart 1 and chart 2 different from the spacing between chart 2 and chart 3?