I thoroughly enjoyed this, enough that I dug out my modified Wii DJ Hero controller that has a microcontroller inside and appears as a controller. With a bit of code to translate the buttons to keypresses and turning my monitor on the side I was able to play. I think it introduced a tad too much lag (or my timing is that bad) but I was able to get into the rhythm eventually. I need a solution for the second level though with four buttons as there are only three on the turntable.
I'll write up a blog post and link it here if I remember.
My only suggestion (which I think would help with keyboards too) is to move the target to the side rather than the top. That way you're using left/right position of the buttons as much as the letters - I had to think whether top was F or J. Turning my monitor portrait helped a lot.