Powering microcontroller off USB, load off wall-wart
Since the digital RGB pixel strand uses a 5V SPI-like interface, and the Teensy 2 is also running off of 5V USB power, then as long as the grounds are connected in common you should be able to run the two off of separate supplies and just route the two digital leads (green and yellow) plus ground (blue) to the Teensy, and the +5 (red) plus ground (blue) to the separate wall-wart power supply.

They give an example of this using an Arduino.

As they mention in their writeup, wire colors can vary from batch to batch so the above instructions may need to be adjusted.