template: customize template value renderer without a function ?

https://snippet.webix.com/zmv3jlz6

I’d like to add a space after the comma when an item of the binded record is an array, without having to use template:function()

In fact, i’d like to override webix array concatenation function

Any hints ? Thank you

Array.prototype.toString = function(){
  return this.join(", ");
}

Thank you intregal