I just did some experimenting with interesting results.
First a review of how the IR cut filter works. In day mode, the IR filter is normally in place between the lens and the sensor to remove IR light which would result in a purple cast. In night mode, the IR filter is pulled out of the way.
Fun fact: you can manually change the position of the IR filter by placing a strong magnet on either side of the camera, regardless of day/night mode. Here’s what I did:
In a totally dark room, I put a V2 in day mode (LEDs off), but pulled the filter out of the way with a magnet. Then I used the LEDs on a Pam to illuminate my face. The V2 was clearly sensitive to the 940nm light from the Pan. I did the same thing using a 2nd V2 for illumination. The V2 was equally sensitive to this light.
Conclusion: you can use a 940nm light source as illumination for a V2, it should work fine, and be less visible to humans than a 850nm source.
Possible hack: Put a V2 in day mode but tape a magnet to the side to pull the filter out of the way. This will simulate night mode with LEDs off. You can then use an external illumination source.
Catches to the above hack:
The camera will be no good for daytime use (purple cast).
Even at night there is a distinct purple cast in this configuration. Apparently night mode also has the function of putting the sensor into black & white mode.