Sorry, it looks like we were wrong about the Teensy libraries working with the A* 32U4. I thought I had it working before because I was able to compile and run one of the Teensy keyboard examples on the A*, but it turns out that example only uses some basic functions that are also defined the stock Arduino keyboard library (which is what the example actually uses when it’s run on an A* or a regular Arduino).
Unfortunately, it doesn’t look like there’s an easy way to use the Teensy keyboard functions on a non-Teensy board, since they’re not actually part of a library; they’re part of a custom “core” that the Teensyduino add-on only makes available for Teensy boards. There’s no reason that functionality couldn’t be ported to the A* 32U4 and other boards like the Leonardo, since they use the same microcontroller as the Teensy 2.0 (ATmega32U4), but it might involve a lot of work and require familiarity with the ATmega32U4 and the way USB HID devices work.
What parts of the Teensy keyboard library do you want to use that aren’t available with the standard Arduino library? I’m guessing you want the set_modifier, set_key, and send_now functions to allow multiple keys to be pressed at once?