Is there a way to do this? (

If the game isn't already programmed to utilize 4 cores (which it isn't), there isn't anything to change that. Back in Oblivion days, there were even members fiddling around with the .ini settings to make the game more multi-threaded, but in the end the game will still hardly making use of more than one core.

Fallout 3 didn't make use of quads either and several members actually had to alter the .ini setting to force the game to only recognize two threads due to constant crashing.

So the Fallout 3 engine uses dual core only? On the back of my retail edition it clearly states "multicore" under CPU requirements, how many cores is this suppose to be?

Here we go again...What exactly makes you think the game is not using all cores? I have a 3 core cpu and even fallout 3 uses all the cores. Have you checked the task manager while the game is running? Even the so called "ini fix" for Fallout 3 never actually made the game use less than all cores. For some reason people are convinced that it did though. The only way to make the game use less than all cores is to set the affinity, but that will only result in decreased performance.

I tried running NV in a window so I could observe task manager in real time while actually playing but it takes over my whole desktop (1900x1200). Then I remembered to change aspect ratio down to 4:3 (1600x1200) and observed task manager, game only uses 4 cores, I disable HT on my quad, its useless in this game. In fact, all the active cores are only running at about 20 - 50 % and I don't have any other applications running apart from OS and its usual stuff.