It seems Leica users are inordinately against flash, and fear that “flashy” look. However, it really isn't that hard to employ the S2 for low light photography without an obvious flash effect, once you get the hang of it.
The technique calls for use of a lower light technique known as “dragging the shutter”.
For example, if shooting ambient at ISO 640, f/2.5, and the shutter is to slow @ 1/25th … set the camera to manual exposure mode with a shutter speed of 1/40th and use the same aperture of f/2.5 … and a SF58 set to ETTL with a modifier mounted on it to somewhat soften the light.
This way you are almost correctly exposed for the ambient, so the background gets exposed fairly well. The foreground then gets the benefit of the additional light from the flash, and the flash duration “freezes” the subject … effectively eliminating hand shake, and in many cases will also freeze subject motion. (At f/2.5 the background won't be sharp anyway due to DOF, so any slight motion there is irrelevant).
Flash duration is how speed-lights and strobes control the level of light hitting the subject. In general, they ALWAYS fire at full power … it is how long they stay on that determines proper TTL exposure. The less additional light you need, the faster the duration is … so by letting in more ambient with a slower shutter speed, the duration of the flash becomes shorter. For example, a typical speed-light that only requires about 1/2 its full duration is 1/1000 of a second. At 1/8th its full duration, it is 1/3,700 of a second!
Try it, it's less disruptive than you may think … the amount of flash is pretty low compared to shooting at 1/125th and making the flash work harder to light the subject.
Again, depends on the subject matter, but this is a viable way to extend the S2 beyond its ISO limitations, and get very nicely exposed images.
Here are some extreme examples using different cameras, but the concept is the same regardless of camera. I chose shots done using low ISOs and very slow shutter speeds … dragging the shutter to simulate using the S2 at low ISOs to keep the noise low.
Color Lips shot: ISO 500 @ 1/25 shutter; Bride being dipped: ISO 200 @ 1/25th; Hands: ISO 200 @ 1/20th, outdoor couple dancing: ISO 100 @ 1/15th. All used flash combined with “dragging the shutter” to shoot where it would have been impossible to do using just ambient.