I got excited when i saw the results since they looked awesome, such that I thought I could replace my quick&dirty transparent GIFs script[1], but apparently it has issues with low-resolution images.

[1] : convert -fill none -draw "matte 0,0 floodfill" -type optimize -colors 64 +dither -trim -fuzz 3% +repage -strip $1 $2

Nevertheless, it's a great technique which i've just saved for such specific cases. Thanks!