When shooting in very low light levels, something the HMC40 doesn't do well, you will have to compromise the image. Test this first BEFORE you do the shoot.
(1) Gain: Most will agree that +12dB is OK, not ideal, but OK. If that's not enough, going to +18dB will compromise the image, but could still be usable. Going beyond that does work, BUT the quality of the image goes downhill very fast. I have yet to find any setting that really solve this degradation in the image.
(2) Shutter Speed: Setting the shutter speed as low as reasonable does help. In low light 1/30 of a second does help when using 60i, 60p, and 30p. In 24P mode, try 1/24 of a second. I have tried 1/15 of a second, BUT the catch is that motion blurring becomes a problem and the movement starts to show a strobe like effect. If you must use 1/15 of a second, make sure the camera is on a solid tripod and you don't move the camera around.
(3) Video Lights: This may not be possible, BUT if you can have a camera light, it will help.