Mine was just a guess without benefit of any analysis. I was remembering my experience with delta-i maneuvers on the DSCS-III satellites. We had two thrusters nominally rated at 1 pound thrust each, but the actual thrust was somewhat less due to attitute control off-pulsing and decreased tank pressures. We'd fire those thrusters for 20-35 minutes to change the inclination of a 2000 pound satellite by as much as 0.2 degrees. Even a small amount of thrust over time can produce significant movement in a massive object.

The Mars Odyssey crew is trying to shave a small amount of velocity on each pass. True, the _peak_ drag might occur over a 4 minute span but the total drag pass will be much longer. Think of a fairly flat "Bell Shaped Curve". The total time that the spacecraft is experiencing drag on each aerobraking pass will likely be 20+ minutes. It doesn't take a lot of force over that time to produce a significant delta-v. I'll grant you that the average drag might be over 1 Newton but I stand by my hunch that it won't be much more than that. Peak drag might be a few Newtons but average drag will probably be 1-2 N.