Having only a non-powered OTG cable and eager to hack my Chromecast, I went looking for other cables/adaptors lying around my house in an attempt to find an alternative. Here's what I came up with.
Things you will need:
NON-POWERED OTG Cable
Male-to-Male USB Cable
1. Connect the micro USB end of the OTG cable to the Chromecast and the other end to the male end of the USB hub.
2. Insert your Flashcast thumbdrive into one of the ports of the USB hub and the Male-to-Male USB cable into another port.
3. Insert the other end of the Male-to-Male USB cable to your preferred USB power source. (I used a portable charger for convenience sake.)
There are many other possible solutions depending on the cables/adaptors you manage to find. The point I'm trying to make is, instead of sourcing for a rare cable days or weeks of shipping time away from you, an immediate alternative might just around the corner waiting for your discovery.