An alternative solution I used on a Suzi DR-Z400 Supermoto was the speaker cable mod. You take sheathed Speaker cable wire (not bare copper) and cut several pieces the length of the handlebar less a couple inches for any bar end or mirror. You coat them with grease (I used waterproof Bel-Ray) and insert them as one through the handle bar.
You don't want to have so many strands of cable that you're stuffing the bar with them. The idea is that they need to move and bounce around as they take the vibrational energy transmitted through the handlebar clamp that they can shake it off like Taylor Swift inside the bar reducing the amount of vibes going to the grips. So the energy of the bike's vibes is used up by making strands of coated copper flop around. The grease will keep the strands of cable from sticking together over time plus make them easy to remove later. (Besides, using grease for your best girl is common courtesy.)
I hated adding weight to the bike (especially high and forward on the bike), but it helped considerably with the vibes of a 400cc Single being wound up at highway speeds. I am not a Z650 owner yet (this is my first post!), but since the bike has a handlebar and not clip-ons, speaker wire is an option.