Is it possible? it seems so
Have I done it? No
How to do it?
you need 3 images.
first one , your main, target image
second one, an image containing your circle in color
third one, an image containing your circle alpha map channel, you could draw a a circle by choosing an alpha specifier color, note that 2nd and 3rd image should be in same manner except 3rd one is only alpha map
blit 2nd image on 1st image using 3rd image as alpha channel, by setting right arguments in blit.
see python s60 documention, blit part, you will understand.
From pys60 doc:
blit(image[,target=(0,0), source=((0,0),image.size), mask=None, scale=0 ])
Copies the source area from the given image to the target area in this drawable. The source area is copied
in its entirety if mask is not given or is set to None. If the mask is given, the source area is copied where
the mask is white. mask can be either None, a 1-bit (black and white) Image or a grayscale Image, and
must be of the same size as the source image. A grayscale mask acts as an alpha channel, i.e. partial