[Plugin: Scissors] Rather than crop, extend background?

This is just an enhancement request. What do you think about allowing a way to shrink an image and then extend the background to meet the thumbnail dimension requirements?

For example, my default thumbnail size is 150×150. I have an image that is 300×450, but all of the image is important for the thumbnail. What I want to do is proportionally shrink the image, making it 100×150, and then add 25×100 of background color of my choice filled in on both sides to make it 150×150.

This plugin is already great, but if this were implemented, I would like it even more. =}