We have a year-old 3-foot Argentine b&w that I've had to "retame" due to lack of handling for a while. I've had good luck with the following strategies:
1. To stop the lunging, don't feed the tegu in its cage (so that it won't associate humans cage food). Get a tall Rubbermaid recycling bin, put the food dish in first, and then remove the tegu from the cage and put it in the bin to feed. For the trick to the "remove from cage" part, go to step 2 -->
2. Wear protective gear, against teeth, claws, and (esp. in your case) long tail. I wear an old leather jacket and "cut-proof" gloves I picked up at Home Depot. If you haven't been handling the tegu for a while, the first few days might be tricky, but don't give up. I had good luck distracting the animal by holding a paper towel in front of its head (which helps you maneuver it sideways), then firmly grabbing it right behind the head and holding it down with my right hand. Get a good handle around the animal's shoulders, get your left hand under it a.s.a.p., and haul the lizard out and hold him firmly (but don't squeeze too hard) to your chest--almost the way you'd hold a baby. The lizard will usually stop whiptailing within a few seconds, though he'll try to squirm forward or backward--keep holding him close, and he'll calm down.
This has worked for us--a month ago, the lizard was snapping and charging anyone who walked in the room. He no longer charges, and has not seriously threated me with an open mouth for a couple of weeks. He still whips briefly, but will now let me actually stroke his back after I put him back down, with only a little huffing (no more jerking or whipping). But you have to keep at it--work with the lizard every day.