DDM bumper lip attachment

[MPoweredEstoril]

I recently bought a e36 m3 front bumper from DDM tuning. I bought the bumper which did not come as a 1 piece set (lip and bumper attached) because I have a perfect lip I want to put on. However, the bumper did not come with holes to attach a lip.
My question is how do I attach a lip to the bumper? Do i simply drill holes, and if so how far apart, size, etc?

[GDS357]

http://www.understeer.com/lipspoiler.shtml

[MPoweredEstoril]

Thanks!