CI2 as a practice/headphone amp?

Sometimes when I want to practice away from my amp, I simply plug my Chapman Stick directly into the CI2, put on some headphones, and use the input monitoring functionality as a simple practice headphone amp. Works nicely, except that it requires that I have my laptop computer nearby.

As an experiment, I tried plugging the CI2 into a wall outlet via a USB charging plug. Unfortunately, that didn’t work.

Is there something I can do to power the CI2 without a ‘smart’ USB port to make use of its hardware input monitoring functionality?

Thanks for any advice.