Well, sort of. I relied on my race car guru, Graham Hatherway. on where to remove weight and drill holes.
We agreed on 10mm diam chamfered holes (to reduce risk of cracking and take extra weight off) for both front and back. Spacing of holes on the front discs was restricted by the grooves (offset front to back faces) so we matched the pattern on the rears just for asthetics. The spacing is designed so that the whole pad area passes over a hole reducing the risk of uneven disc and pad wear.
The exercise is purely one of weight reduction. Any dust extraction properties of the holes would be a bonus, but not looked for.
I must have made a mistake in earlier weighings, as the total saving is 3.2kg, or 800gms per disc. Not as much as I was hoping for but significant, none the less.