Sorry for the delay, got hung up at works quite late the last 2 days.

Anyways, since you can get the problem to occur pretty consistently, that's a big help. You'll need a straight, fairly smooth road with minimal traffic. Drive the vehicle and apply the brakes in a fashion that makes the problem occur (hopefully under 30 and not a panic brake situation)

when doing this, take your hands off the steering wheel (keep close and ready to grab)

Note wether the steering pulls to one side or the other when the pedal starts to shake (abs kicks in)

The abs will release the brake on the wheel it thinks is slipping, this means an imbalance from side to side. The side that still has brake will pull the steering that way. Basically if the steering pulls right then the left front sensor is suspect.

Do this a few times to rule out road conditions, if it always pulls the same way on braking that kind of confirms it. If it pulls a different way each time well this doesn't work.

No pull? possibly both front sensors are no good, or the rear sensor or?

This all assumes the vehicle drives straight and true to begin with.

If the above test is inconclusive, you will need a scanner or have to shotgun it.