Yes, you are right on the first point. By changing the steering axis offset, you can increase caster and still have zero mechanical trail. I think that you would have to redesign the steering system of the car to achieve that though.
I think that what I meant to say didn't come across right on my point about feedback. Mechanical trail and pneumatic trail added together gives total trail, which directly affects the torque required to turn the steering wheel. However, the forces produced by virtue of the pneumatic trail are non-linear and dependent on tire characteristics. The forces produced by virtue of mechanical trail are linear and proportional to lateral force. Therefore as mechanical trail increases, driver feedback from the tires (pneumatic trail) gets drowned out. I am not saying that the actual pneumatic trail decreases, what I'm saying is that the effect from it is lessened since mechanical trail dominates (as caster increases with steering axis offset held constant).
Thanks for the correction.
Leon