This may not be the answer you are looking for, thinking outside the box, (the box being the camera) may help you overcome the situation and obtain the image you want if no other option is found on time.
I use a Canon 50D and when I face similar situations, I add to the equipment a small but powerful L.E.D. torch or flashlight. It is small, powered by 3 AAA batteries.
What I do is illuminate part of the subject for focusing purposes. I do it either for live view manual focusing or even to enable auto focus on very low light situations. This can be done from the camera's position, but you can also have a friend stand close do the subject and illuminate it for you while you focus. Just tell them to hide (and turn of the light) before shooting
Of course, there are subjects that are too far away to use this trick, so depending on what is it I have two alternatives.
For starry skies or cityscapes, I use one of the light dots as a focusing reference. A reflection on a shiny object can do too. What I do is focus back and forth while looking at a bright dot. When it gets out of focus it looks like a disc, so I move the focus trying to get the disc as small as possible.
For completely dark scenes, I Use manual focus, try to focus and then intentionally defocus a little on certain direction. Then take several shots, but making very little adjustments to the focus ring in the opposite direction between shots. Repeat until you know that you are definitely out of focus again. Then select in post the shot that has the right focus. (This is some sort of focus bracketing).
A third option is to use focus scales. This are focusing markings that where mostly found in old manual lenses, so that if you knew the distance from subject to camera, you could focus by setting the lens to the corresponding marking on the focusing ring. However it is very unlikely that you have one of these lenses. I don't have one, so I make it.
I simply adhere a couple of stickers to my lens. One on a fixed part of the barrel an the other on the focusing ring. If I can access the scene during the day, then I go in that time, focus, and make the necessary markings. If not, I can calibrate the focusing on various distances by intentionally placing objects at measured distances from the lens.
However, this only works for lenses that have a solid linkage between the focusing ring and the corresponding elements inside the lens, and specially with prime lenses. On most zoom lenses, it works only for the focal distance used when the markings are made.
Bear in mind that some lenses may be sensible to temperature changes, so they can be out of focus even if set on the correct marking, so, combining this method with focus bracketing is advisable.
I have a better description of these tricks on this answer: How does one get manual focus right with a fast-aperture lens?. The question itself is relevant and other answers there may help you.