Since so many people are talking about throwing on sliders, let me just point out something:
The two holes needing drilled out for the Novatouch sliders are dual purpose: they also allow the keycap stems to drop below the mounting surface, so you can, you know, actually depress the keys.
So, even with the JTK sliders, the MX return and shift keys still won't work without modification to the keycaps themselves.