Brad also came through with an Arduino motor shield, but I'm not quite ready to start soldering to the board. I'm found some Arduino 6 and 8 pin spacers, so I'm going to wait for those to show up before getting started on driving the 2 motors.
I've also started reworking the notification logic. We started with a constant notification logic. Whenever something was in range of the sensor, we would drive the motor. We then increased the motor speed with proximity. This didn't work well in practice. The motor wasn't big enough to give good gradation over the range, and the always on quickly became annoying. It stopped being information.
The new logic plan is to have 3 zones: near, medium, far (and technically a fourth -- out of range). Each zone will have an initial notification pulse, and then a delay. Basically, if an object remains in the same zone or moves to a further zone, we will skip a couple of notification cycles. I didn't get very far on thtat. That's this weekend's project.