Don't know that I'd want to do the hill at the 40 mile mark from NY. But one could also take the bike on Metro North (gotta get a permit, cheap) on Sat & Sun up along the Hudson and get off right near Bear Mountain Bridge at Manitou (slightly north) or Peekskill (slightly south, though more crowded). Then, hit the mountain and ride back in to the city, which should be every so slightly downhill. Or ride around all day in the area and take the train back.
I used to do this all the time in the mid-90s with my mtb. Nice ride up the Hudson, nice towns all the way from Peekskill to Cold Spring.
Here's Metro North bicycle regs:
http://www.mta.info/mnr/html/getaways/bikerule.htm
Way better than riding the loop in Central Park!