Well, boys (and girls), I think I've got it.
I put a 4.7 uF capacitor in, like the schematic above, and after tweaking the value of the resistor in parallel with the cap, I got a funky looking signal like this:
More importantly, I was able to use the oscilloscope to measure the time of the "peak" part. 2 ms, or 2000 us. Once I set the injector delay us to that, I got (what I believe to be) a fairly realistic reading. It didn't change too much with RPM, but when it did, I think it was an actual fuel consumption increase.