I just recently got a Birdy, and have the same issue. One (expensive) option is to get a Syntace VRO set. You can get them from Thor USA:
http://www.thorusa.com/dahon/accessories/handlebar.htm
It is also listed on the Dahon homepage, but doesn't appear to be for sale:
http://www.dahon.com/components/xp/radiusvro.htm
I say expensive, because for your $48 you only get an additional 30 mm (just over 1").
You're probably better off getting a riser bar of some kind, if you can live with the fact that most of them have a slight sweep backwards..