I had some pipe in my shed the same size as the spacers so I cut off a short length, sharpened up the leading edge to turn it into a punch, then put a bolt through the punch and into the frame, tightening down on the bolt had the punch cutting through the plastic very easily in the exact places required.
I did use longer bolts than the Givi supplied bolts when I did my install & with one on each side I was able to back up with a nylock nut to ensure things stayed in place.
Some of the 19 rides in my shed
2014 V2, Snoopy
2009 Wee, Pumbaa the pig
WR450F, The Blue Postie Bike
YZ250N smoker with rego, Stinky.
Yamaha MT09 (FZ09), The Scud missile.
Club Lead not Club Med.
He with the most toys wins.
Out of my depth in a puddle.
Live life on the edge you will see more that way.
Ridding a motorcycle keeps things in balance.
At the end of each trail and at the end of each day history is made.