Anyone know how best to deal with back-focusing in low light?

Was out at a birthday party last night with my 5n, Sigma 30 and F20S flash. The lighting was very poor and even on the LCD it was difficult at times to make out the subjects. However, when focusing, about 50% of the time the camera was locking onto something far away and not what I was trying to get in focus. I realize I could use DMF to adjust, but the focus ring on my Sigma is extremely finicky and difficult to use. I guess the next time I might just use a manual lens in very low light scenarios. Only problem is trying to explain to other people how to use DMF when borrowing the camera.

Anyways, anyone figure out a way when auto focusing to help get your subjects in focus, the first time? I was using P mode and had face detection on, which helped a bit. Also the AF mode was multi, perhaps use center?