definition of cheap bastard. lol.
As a more reliable* backup, perhaps you could also make a self-contained battery powered adapter. Use a rechargeable cell phone minty boost thingy to power it. Just hack a USB cable to have a male USB plug to plug into the portable battery powered supply, then a male micro USB to plug into the phone, and then w/e plugs you want to plug into the USB device (or just a standard female USB jack, where you can plug any number of cords)? Insta 5V and the boost converter, low battery cutout, and charging IC are already built in. Plus you can charge your phone with it, using a regular cord if necessary (the data lines on the charger are probably shorted together, so don't connect them between charger plug and the rest of the adapter cord.
the adapter cord may or may not be able to utilize the full output of the charger without those data lines connected. You could always put in a switch to short them, if this is the case, to make your cable multi-purpose.
*Just a hunch; no offense. Soldering a few wires together is a lot easier to make reliable, with enough hot glue and tape, than building a custom DC converter and trying to fit and hand-jumper it into a cell phone.
Food for thought: you definitely don't have room for a switch in there, either. So if you are a guy that habitually runs out of batteries all the way to shutdown, you should probably have to locate a power rail in the phone that cuts out when the phone shuts down, else you run a risk of ruining your phone battery if you wire it directly to the battery outputs.