transparency brush

don't know if this is possible but it would help to have a transparency brush in doing fades on curves.  the brush would enable to lighten spot colors when brushed over the curve or curves.  you could make a whole graphic fade out around the edges just by brushing over the edges.  you could have the capabilities to adjust the amount of the fade on a tool bar.  maybe this is out there,  but it would save a lot of time when doing graphics for t shirts and you want to fade the edges of the image on the shirt.  you rip program would define the half tones by the transparency fade.