Probably not. The power out to the USB ports is monitored and limited, so you may not be able to feed power back in reverse.
The tracks may not be capable of carrying the full load current.
Even if that much works, the Pi will not start up with only that power source.
Also, feeding power in through the full-size USB connectors bypasses the polyfuse protection, so your Pi is more likely to suffer serious damage if something goes wrong.