It's not the same as an overall widening effect, but you can get some useful control over an instrument's stereo width using the Mid and Side modes in ColoringEQ or any other EQ that supports them. For instance, if you want to push a stereo background pad (or a big reverb, even!) out of the way of a center-panned lead melody, you can cut the conflicting frequencies in Mid mode, so it steps out of the way in the center but retains its depth on the sides. If you want to give some cymbals more width and add some presence without conflicting with your centered foreground elements, you can boost their high frequencies in Side mode. Etc, etc