They were smaller (1/2" or so) bubbles in a sheet I got from Murph with a shipment, so he might sell ya a sheet...
You couldn't see the bubbles though. The Gaff tape (basically black duct tape) was wrapped in such a way that you couldn't see the bubble wrap, and I wrapped the bubble wrap in the direction of the throttle twisting, so it wouldn't unravel as I applied throttle. Actually worked quite well for a few weeks, until I removed it to install the gel grips.
These days, though, my Connie is rather bruised from a few falls, so the cup idea may be in order...