Knott, I needed to be able to push my B72 on my touring bike back about a cm. and finally found a solution. Clever Cycles recommended the Brompton saddle adapter pin, so I switched to that coupled with a straight seatpost. I've only ridden it a couple of times so far but the times I have been on it my right hip and knee have been so much happier. And so has my pocket book! The lugged seatpost with extra setback at Riv is a looker but more than I wanted to spend.
Taken from Cleverchimps flickr page:

Link to Google products page:
http://www.google.com/products?addr=...wQrQQwAg&sl=on
You might try asking if your LBS can order it for you or see if one of the folding bike shops have it in stock.
Everything in moderation, including moderation.
2007 Rodriguez Adventure/B72
2009 Masi Soulville Mixte/B18
1997 Trek 820 Step-thru Xtracycle/B17