You don't re-drill a rim for extra spokes. You're going to have a drastic effect on the structural integrity of the rim not to mention if you do try it and the holes you drill are spaced in the gap unevenly and/or not properly aligned with the other spoke holes will render a rim useless.

I know that it's been done with bmx and some mtb's. Thankfully that stuff stays in trials bikes. There's a reason that stuff vanished on the xc and dh aspects in mtb's. The stuff wasn't strong and the advancement in materials that are lighter and stronger than the materials of old have rendered speed holes obsolete.