Do this. Get these items.
-Couple of wooden round sharp pointed toothpicks.
-A pin or needle, metal with a good point. Large sewing needle is best or an auger tool of some kind with a small metal bit like a pin.
-Superglue gel or better yet, Bondini brand, as it is thick like model glue, but thinner than plain SG gel
- Super glue fix (can be found at most hobby shops) Either small drip bottle or spritzer bottle will work. It dries fast and won't ruin paint.
-a plastic container lid or something to drip glue into that is expendable.
-the precut and prepared quills, some longer than others.
-pair of tweezers and maybe a needlenose pliers
-gloves if needed (I get SGlue on my fingers all the time, so I go barehanded, Sanding pad will remove dried glue from fingertips...)
- Time
-Patience
Do this routine, ONE HOLE AND QUILL AT A TIME! Do not rush!
1st- take Pred head, use metal pointed tool or pin, may need to hold with pliers to get enough leverage and push into desired hole spot ( start at the back of the array of quills, and work over them so the overlap effect will work properly, always back to front)
2nd- after making said hole, insert rounded tip toothpick into the hole, twist it down into the hole enough so it is for sure wide enough to accept your trimmed quill when the time comes. Important! Leave the toothpick in place until you are ready to set the quill so as to allow the rubber to stay open enough to receive the quill. The holes tend to close after you remove any hole making item. No need to drill out holes! Let the rubber/pvc/vinyl help hold the quill in place. You'll see!
3rd- on the expendable plastic container lid or temp surface you have handy, put a nice drop of glue, deep enough to dip a quill into to just coat the inserted area of it.
4th- Using tweezers, grasp the quill by the sharp tip area, get it situated so it will go into the hole the way you want it to, right angle etc. and dip the inserting end of it into the glue drop, deep enough to coat the part to be inserted only, no deeper.
5th, At this point, on the Predator head, remove the round toothpick, set aside quickly, and set in place your quill. After a couple of seconds, the hole will close up some, around the glue and help hold it into place.
You can spritz the area with Super Glue fix if you need, but I would after setting a couple to save time and material.
Continue until your quill arrays are done. Try to work the shortest ones at the ends, front or back of your arrays. I even trim down the very edge ones so there is some variety in the lengths so as to look more organic and less the same. Always trim away from the wider base, and not the sharp tip!
Take time to make sure they are pointing where you want them too, and before the holes fully close, you can adjust them some. They should be pretty well set after the glue sets. Not that easy to break off.
Repaint tips if needed, but only if you are sure.
That should work. Does for me.
Best of luck!