You will need a cheap micro USB cable ... the cheaper the better because you will be cutting out the micro USB connector with a razor knife (x-acto works just fine). Then you need to go to a Radio Shack and buy the 5-pack of 100K ohm resistors for $1.29 (you only need three, but 300k single resistors are harder to find) and a soldering iron with a fine point.
Slice the insulation off the cable and disconnect all the wires. Then you will need to solder the three resistors in series and connect the ends to pin 4 and pin 5 of the micro USB connector.
The connections will be (when viewing the connector as shown) the furthest most left connection on top (pin 4) and on bottom (pin 5)
You end up with this:
Once you've built your jig, then power off the phone (battery pull would be advised in your case) then with the phone off, plug in the jig. In a few seconds it should boot into download mode and away you go.