First, the unit that you linked has only 5 magnets - not a good choice. Go for a 12 magnet unit that will allow you detect start/stop pedaling with less crank rotation.
Next, there are two types of PAS units - with either one or two halls. The incredibly cheap models have a single hall and pulse when pedaling in either directon. The better models use the second hall to condition the output so you only get pulses in the forward direction. Unfortunately, in your case you wish to actually get a signal in the reverse direction AND be able to determine direction.
However, if you start with one of the better 2-hall units this capability is easy to obtain by bypassing the internal logic (which is pretty simple-minded) and routing the output of both raw hall signals to your uproc directly. You can arrange/leave pull-up resistors in the sensor head or add them to the chip input ports.
Here's a post
about doing that mod on my Mundo build.
The two halls are offset less that the inter-magnet offset and so generate a quadrature signal like this:
As you can see, it's pretty simple to determine the direction by using the RPM signal to enable logic that looks at the direction of transition of the DIR signal (i.e. scan the image right-to-left (REV rotation) vs left-to-right (FWD rotation) and eyeball the red line transition only while the green is high).