Android ATtiny arbitrary data communication over USB
There is no easy way to do usb host and charging at the same time. Most phones do not support this. 

But you can bypass the need for usb communication by using a bluetooth to serial module. Nothing really changes on your ATtiny aside from some minor configuration.  Same serial port as the FTDI.  Then provide power as a normal usb connection. 

V-USB acts like a FTDI or other usb serial IC, so Android Host Mode is still required.