Hi toe_head2001,
I know this is a really old topic, but I believe there is a way to do this via the GUI assuming the control box is relatively rectangular. The first step would be to expand the canvas size before calling up the plugin. This may be necessary if you're working right at the edge of the image. Next, open up the plugin and set the control points tight to the area you want to correct. Then, adjust each control point value as follows where P = amount to pad; upper left (x-P, y-P), upper right (x+P, y-P), lower left (x-P, y+P), and lower right (x+P, y+P). This could be implemented in the GUI by allowing the user to enter the number of pixels to pad and buttons to add or remove the padding prior to clicking okay.
As for myself, I would like to see a way to increase the size of the GUI box so that the control points are more visible. Someone mentioned zooming in to set the points, but I think a bigger overall box would be more helpful. Hope everyone has a great 2024!