Well either by the guests/drivers showing confirmation info to the official when coming in or going out, as
tránsito suggested would be the case at one point during the meeting, or just as they are handled on 4th street or 5th Ave or in other places not accessible by car, namely on foot. As Claudine of Alhambra pointed out (quite correctly), there are numerous places in Mexico as well as in Europe where hotels are not accessible to the public by car and people traverse pedestrian zones to get to them. (Again we don't see that as the way to go, but others apparently do.)
Another... well,
intriguing argument for the change from the side in favor of it yesterday is that it would supposely raise property values.
Edit: In fairness and in relation to that last point, perhaps, I should add that I think some of the reasoning for the move is based on the idea that the restaurants and shops or other little businesses on the street will benefit in the form of increased traffic (pedestrian, obviously, not vehicle) and thus increased sales or whatever. So for examplethe restaurant in the alleged "cursed" spot (as discussed on the "openings & closings' thread by others recently) might find itself with more customers or whatever. Personally I think it's the nature of the lsidestreet ocation in general and all the competition on 5th itself that slows business to such places, not whether cars are parked along the sides of the businesses, so I see that view as misinformed or perhaps optimistically naive. But it's a view, and just to mention it.
Steve