No, you can't. The usb is basically a microphone interface.
If you are looking for something that can be powered via usb check the zomm pedals (b1on, b1Xon, b3on...)
the plex is treating me well so far, i like it. It's okay if they don't want to update anymore but they could give the code source away so we could fix it ourselves! Any one has any contacts with them?
Just got my GK Plex. Didn't have a lot of time to try it but the sounds sounds good but heard some white noise.
It's a a03 revision should update the firmware?