@Sneaksie - You've made an old man very happy
@jbailey - Just for future reference, all my reading around the Web says this is not possible. I tried it anyway
Even if I take the game files out of the Steam directory and put them in a "spoof" file structure (mimicking the original NVN) the patch executable still believes the game is not installed. I draw the line at mucking about with regedit.