The no diode route means more wires - you connect one pin on each switch together and to a Teensy pin, and another wire from a teensy pin to each switch's other pin.
Firmware wise you should just be able to call it one row with lots of columns, there was a problem with EasyAVR where it didn't like having less than two rows but that was before the rewrite so might work now and if not you just configure a fake row with nothing connected.