here is a new upgrade. i did not want any homeless guy stealing my handlebar or seat and seat post. so i added a seat post lock. both are standard 35mm size. it works great on the handlebar post and takes a while to adjust on seat post but can get it to work. the owner says dahon called him lately to perhaps make a option on dahons out of it. they are $20 each.
http://www.saveyourseatlock.com/