[NTG-context] Stretching width in natural TABLEs

Hi, Is it possible to stretch the widths of each column in natural TABLEs, so that the widths are in a certain propotion? For example, suppose I have a table with three columns and I want to set the width of the first column to a fixed amount, and split the remaining space between columns two and three in a 1:2 ratio. Extreme tables implement something similar using option={stretch, width}, but AFAIU, it is not possible to fix the width of a particular column. Aditya