jQuery Grid Plugin - jqGrid

Currently I have implemented a small script, which lets me resize grids by setting its width to a percentage of the width of its parent.

So, when the browser is resized, the grid is resized automatically. Of course, resizing does not apply to the columns, this would require calling setgridwidth on every resize of the browser (like fluidjqgrid does), which I want to avoid. 

As an alternative, I would like to provide the user a button, to resize the columns. But I don't want to call setgridWidth, because this sets the grid's width to an absolute value, and I want to keep the relative size.

Is there any way to set the grid columns width, without calling setgridwidth?