I have several injector devices that have come with wireless AP points, cisco phones etc. They are a rect block with a eth in, power in from a wall wart (like that came with the ETD) and a eth out. should be able to use one of those on the ETD end but just in reverse, instead of the power in, it would be power out to the ETD. Just need to make sure your polarity is correct. Depending on the wall warts barrel connector, you should be able to use it to inject the power on the source end if the connectors are the correct size.
I am thinking of something like this as well when the conductor/slave are finally avail. Depending on draw etc, am hoping to power the ETD and a wireless bridge this way via single eth cable vs eth cable, power cable for ETD and power cable for wireless bridge.
Myk