Hey fellas. I had the same question and Bruce sent me this reply in a support email:
No problem with shortening the Mag-Volt. First, roll the small silicone o-rings away from the magnets on top. Then pull the silicone tube off of the nipples and cut to length with a sharp pair of scissors or box cutter. Reconnect the tube over the nipple and roll the o-rings back into position next to the magnets. Be conservative with the amount you remove and test before deciding to make it shorter again.
Props to Bruce for always having helpful feedback!