I did the same thing this past winter.
You can't cut teeth into the balancer. The balancer is so wide that you will get an erratic signal. Look at a stock part - the toothed wheel sticks out further than the edge of the balancer for exactly this reason.
Adding a wheel to the front of your current balancer is not that big of a deal. You will have to add spacers to the other pulley components. Again, not a big deal. You can carve them out of some 1/8" alum without too much difficulty. I did it with standard hand tools.
Or, you might get lucky and find a stock balancer that will work for you. Then you could get the factory bracket and sensor, too.