Except you've got to make clearance for the twist throttle grip so it does not grab on the mirror plug.Make them tight for the mirror stems, to reduce the opportunity for water to get into your bars.
Yes thats the best way. Trying to cut with a razor knife never seems to do a good job.I took an appropriately sized piece of copper pipe, filed the edge to a point and used it as a punch on the end of the grip. Made a dandy, correctly sized hole for the bar ends I used.
FYI: Direct image attachment is reserved for VIP-quality folks only. Those in steerage class must upload to external image hosting sites first, then a link can be placed here.Advise your friend that the method of securing bar-end mirrors can be greatly improved by fitting a proper anchor bolt, (aka "Rawlbolt"). I found it necessary to open up the manufacturer's bolt hole a little with a drill bit to take the new bolt. The original mounting mechanism is distinctly Michael Mouse, and the mirror is now solidly secured and pretty much blur free. Highly recommended.
I've tried to attach an image (JPEG file) of an anchor bolt but haven't yet figured out how to - most odd...