How to bind widget image dimensions to variable

I have a certain widget that contains a widget image of a bar. I would like that bar to vary in length depending on certain variables. The brush image is configured as a box, so that it still looks good when stretched. However, the position of the image has no bind button next to it.

Does this mean that I can not bind the dimensions of an image to a variable or can that be achieved in a different way? Is it impossible because the stretching of the images can not be done during run-time? Are there any workarounds or alternatives? Thanks in advance.

Here is an image of the widget inside the widget editor:

Already figured it out myself by means of the following post: variable driven widget size