I could be wrong here as I don't have a good means to mess around with or test the coordinates, but if you check the triggers_pit.xml file for each track located at \F1 2012\tracks\circuits\[track_name]\route_0 you'll see coordinate entries for "rear_wing_timing", "rearwingtiming", "rear_wing_timing_1", and "rearwingtiming1" down near the bottom of the file.
I'm going to guess those are the coordinates where the AI uses DRS, though I'm not sure the difference between "rearwingtiming" and "rear_wing_timing" coordinates.
Interesting side note -
If you check the triggers_pit.xml file for Monaco, at the very bottom you'll notice a section for "rear_wing_forbid". This also is true for the triggers_pit.xml file for Spa. These coordinates would be for the tunnel at Monaco, and Eau Rouge at Spa, where you're not allowed to use DRS.
So somehow you will need to edit the coordinates so that only the
race DRS zones are
not in that "rear_wing_forbid" section, and the rest of the track is. Maybe it's as simple as the "rest of the track" being the coordinates found in the other coordinate blocks in the triggers_pit.xml file...?
I just hope you can add the "rear_wing_forbid" portion to trigger_pit.xml files for tracks that don't normally have sections where DRS is forbidden, as this seems to be the key to making DRS act as it does in 2013.
Hope my 2 cents winds up being worth more than 2 cents