I have the Sapphire Falls (basically the same thing) and I've used it on my husband but I never take my hand off of it.
I'm planning to buy the silicone vibrator enhancers that EF began selling recently. I think these would not only allow us to use toys solo that don't have a flared base but also make the toys easier to hold onto during couples play.
The bottom bubble on this is larger than the bubbles on the shaft, so it acts like a flared base for the toy. It depends on how much larger you need your base to be, but this one is 3/8" diameter larger than the bottom of the shaft.