You get creative.
NY has a great canal system, and camping is allowed on most of the canal banks.
Asking permission is usually better than just planning to hide. If you're bold enough, ask at churches and fire stations and police stations. If you see someone standing on their spacious property, ask if you can set up a tent for the night in their yard or if they know of any other place. Ask "if you can set up a tent" rather than ask "for a place to camp." If you ask the latter, people tend only to think of campgrounds. Also, you might ask where you might set up "that nobody will mind," which gets them thinking more broadly rather than just places where people normally camp. Promise that you will leave first thing in the morning.
If asking fails, then look for any out-of-the-way place, not subject to a lot of people passing by and not close to any inhabited buildings. Wait until it starts to get dark and everybody goes home before setting up. Consider baseball fields, swimming pools, public parks, behind municipal buildings. If the grass looks lush, look out for sprinkler systems. Consider sleeping under cover without setting up a tent, which allows you to get in and out more quickly and be less noticeable. Under bridges, on the porch of public buildings, under a shelter in a park, etc.
More ideas can be found at:http://www.crazyguyonabike.com/doc/stealthcampinghttp://www.crazyguyonabike.com/doc/3952https://www.crazyguyonabike.com/forum/board/message/?o=1&thread_id=461835