My wireless rotary with built in powerpack

[Sekt]

If it were me, I'd use one of those lithium polymer batteries for model helicopters (long as their safe) and maybe use Velcro armband to attach to arm or even shoulder of Tattooist. Then have an RCA lead coming from arm/shoulder powerpack. You'd have to make sure power pack gives a warning, and shuts itself down if it goes below three volts.
That way, the weight is not on ones hand/fingers, its mobile, and use with any machine. Those lipo batteries should go forever. Then use voltage regulator (or ESC to regulate the motor speed no matter what the battery state or motor demand) with adjustable voltage button/knob/display etc. Oh an send me a cheque when you make some cash lol!