The "stupid" Porsche engineers didn't drill a hole in the brace plate, because the stability of this brace plate is realy important. It stabilizes the rear axle. And because it is made of alumiunium the material can get weak over years if you harm the structure by a 2" hole.
Maybe you should install something like this now:
http://www.rennline.com/Cayman_Boxster-Tie-Downs-Stabilizer-Bar/products/1067/
Or as an alternative:
http://986forum.com/forums/99433-post29.html
http://986forum.com/forums/99785-post32.html
Complete thread:
http://986forum.com/forums/general-discussions/10817-driving-impressions-lower-stress-bar-2.html
Or another option:
http://pedrosgarage.com/Site_2/TechnoBrace.html
BTW: how can i link to a position in a thread?