What is the goal? You want to run the teensy from the LiPoly? To do that, you would need something like a MintyBoost to get the LiPoly output voltage back up to 5v. Similar to this
, except without the solar.
Build the MintyBoost, but skip the resistor network on the data lines (R1, R2, R3 and R4). Connect as in the solar project above - except your power source will be USB instead of a solar panel. Finally, connect the ground lines from the charger & the Minty and jumper the data lines from the charger to the Minty. It will be tricky to solder to the data lines on the mini-usb. If you have room, it might be easier to cannibalize a USB extension cable and tap into the data lines there.