Unfortunately, it doesn't look good. You need to actually read the exact wording of the regulations as it gives a lot more clarification as to exactly what they say. The generic version makes it sound like you have a choice of one of the three while the actual written law sounds like it;s all. This is the actual written law for that section:
A pickup truck which is used exclusively for non-commercial purposes with an unladen weight over 5,000 pounds, with no business advertising, with the bed completely enclosed by a camper top, with at least one side window in the camper top, and with seats, seat fittings or camping equipment mounted in the bed, may receive a passenger registration, at the registrant's option. These modifications must be permanent. Camping equipment means that a bed, stove or refrigerator must always be in the vehicle. Any use of the truck without these modifications requires the vehicle to be registered as a commercial vehicle.
15 CRR-NY 106.6
NY-CRR
Current 2018
So it sounds like you must have no commercial advertising, AND a cap with two windows on the sides, AND a sleeping bed, refrigerator or stove in the pickup AND those items must be permanently mounted. So it appears a fifth wheel hitch in an open bed will not be sufficient to make it a passenger registration.
