I agree with Bob.
Run it through NetFabb first an than bolean subtract the fixed object with your object as the hole.
for instance like below
module yourhole () { // a circular shaped hole module
translate (v=[x, y, z]) // put the hole in the right position
rotate (a=[x, y, z]) // put the hole in the right direction
cylinder (h=5, r1=3, r2=3); // the hole itself
} // end of module
difference () { // start the subtraction
import ("object_fixed.stl"); // the original fixed object
yourhole (); // the module that builds your own hole object
} // end of the subtraction
www.3daybreaker.blogspot.com
Orca V4.4 rebuild to Ramps with Mk8 and E3D, as well as a Rostock Delta Mini and an OLO in backorder :-)