Yeah, I guess this is a better idea. However, to park in the RR lot at Syosset, you'll need to apply with the Town of Oyster Bay for a parking permit (about $15-20) and then get to the station no later than 7:00-7:15am. The stores in the downtown area will have you towed if you try to park in one of their lots, or even on the street in front of them all day. Neighborhood street parking near the LIRR is usually restricted until after 10:00am.

The Long Island Expressway Service Road, probably your straightest, quickest route toward Manhattan, is a couple of miles south of the railroad station. Perhaps you can find parking in one of the neighborhoods near the LIE and then jump on the bike from there. If you end up taking the train back to Syosset, you'll just need to ride that short distance to pick up your car.

Before you attempt my route that uses the LIE Service Road to the Cross Island Parkway Bike Path, etc., you need to make sure that little side path off the Northern Blvd bridge in Flushing is still there. Otherwise, you're going to have to brave one of the busiest sections of Northern Blvd to get over to the Flushing Bay Promenade and onward toward the 59th Street Bridge.