Here's how I did mine with some leftover clip on type bar end mirrors:
Took off bar ends so I could eyeball the width of the spacers I needed to cut.
Cut spacers and installed inside the grip.
Reinstalled bar ends with clip on mirrors...checked for free play on throttle side. Very important that the throttle not stick for obvious reasons.
Materials: Extra Vortex clip-on tube I had (approx. cost new $6.00)
Tools used: Hacksaw, file, 8mm and 4mm hex head t-handle.
Time: 20 minutes or so