Not a simple or built-in way.
First, you need to capture the Spriteset to a bitmap. (There is a "screenshot" script around here somewhere.)
Then, use a convolution / blur algorithm. Basically, for every pixel in the image, average the color with all pixels in a given radius (or square). For example, you have a red (255,0,0) pixel surrounded by 8 blue (0,0,255) pixels. You change the red pixel to (28,0,227). Use the get_pixel & set_pixel methods from the Bitmap class.
That help?